Handel's fixed point theorem revisited

Michael Handel proved in [7] the existence of a fixed point for an orientation preserving homeomorphism of the open unit disk that can be extended to the closed disk, provided that it has points whose orbits form an oriented cycle of links at infinity. Later, Patrice Le Calvez gave a different proof of this theorem based only on Brouwer theory and plane topology arguments [9]. These methods permitted to improve the result by proving the existence of a simple closed curve of index 1. We give a new, simpler proof of this improved version of the theorem and generalize it to non-oriented cycles of links at infinityComment: Ergodic Theory and Dynamical Systems, Available on CJO 201

Lack of increased availability of root-derived C may explain the low N2O emission from low N-urine patches

Urine deposition on grassland causes significant N2O losses, which in some cases may result from increased denitrification stimulated by labile compounds released from scorched plant roots. Two 12-day experiments were conducted in 13C-labelled grassland monoliths to investigate the link between N2O production and carbon mineralization following application of low rates of urine-N. Measurements of N2O and CO2 emissions from the monoliths as well as δ13C signal of evolved CO2 were done on day -4, -1, 0, 1, 2, 4, 5, 6 and 7 after application of urine corresponding to 3.1 and 5.5 g N m-2 in the first and second experiment, respectively. The δ13C signal was also determined for soil organic matter, dissolved organic C and CO2 evolved by microbial respiration. In addition, denitrifying enzyme activity (DEA) and nitrifying enzyme activity (NEA) were measured on day -1, 2 and 7 after the first urine application event. Urine did not affect DEA, whereas NEA was enhanced 2 days after urine application. In the first experiment, urine had no significant effect on the N2O flux, which was generally low (-8 to 14 μg N2O-N m-2 h-1). After the second application event, the N2O emission increased significantly to 87 μg N2O-N m-2 h-1 and the N2O emission factor for the added urine-N was 0.18 %. However, the associated 13C signal of soil respiration was unaffected by urine. Consequently, the increased N2O emission from the simulated low N-urine patches was not caused by enhanced denitrification stimulated by labile compounds released from scorched plant roots

The legacy of microbial inoculants in agroecosystems and potential for tackling climate change challenges

Microbial inoculations contribute to reducing agricultural systems' environmental footprint by supporting sustainable production and regulating climate change. However, the indirect and cascading effects of microbial inoculants through the reshaping of soil microbiome are largely overlooked. By discussing the underlying mechanisms of plant- and soil-based microbial inoculants, we suggest that a key challenge in microbial inoculation is to understand their legacy on indigenous microbial communities and the corresponding impacts on agroecosystem functions and services relevant to climate change. We explain how these legacy effects on the soil microbiome can be understood by building on the mechanisms driving microbial invasions and placing inoculation into the context of ecological succession and community assembly. Overall, we advocate that generalizing field trials to systematically test inoculants' effectiveness and developing knowledge anchored in the scientific field of biological/microbial invasion are two essential requirements for applying microbial inoculants in agricultural ecosystems to tackle climate change challenges

Light Emission in Silicon from Carbon Nanotubes

The use of optics in microelectronic circuits to overcome the limitation of metallic interconnects is more and more considered as a viable solution. Among future silicon compatible materials, carbon nanotubes are promising candidates thanks to their ability to emit, modulate and detect light in the wavelength range of silicon transparency. We report the first integration of carbon nanotubes with silicon waveguides, successfully coupling their emission and absorption properties. A complete study of this coupling between carbon nanotubes and silicon waveguides was carried out, which led to the demonstration of the temperature-independent emission from carbon nanotubes in silicon at a wavelength of 1.3 {\mu}m. This represents the first milestone in the development of photonics based on carbon nanotubes on silicon

Optical Gain in Carbon Nanotubes

Semiconducting single-wall carbon nanotubes (s-SWNTs) have proved to be promising material for nanophotonics and optoelectronics. Due to the possibility of tuning their direct band gap and controlling excitonic recombinations in the near-infrared wavelength range, s-SWNT can be used as efficient light emitters. We report the first experimental demonstration of room temperature intrinsic optical gain as high as 190 cm-1 at a wavelength of 1.3 {\mu}m in a thin film doped with s-SWNT. These results constitute a significant milestone toward the development of laser sources based on carbon nanotubes for future high performance integrated circuits.Comment: 4 figure

Ultra-compact on-chip metaline-based 1.3/1.6 μm wavelength demultiplexer

International audienceIn this article, we report an experimental demonstration of enabling technology exploiting resonant properties of plasmonic nanoparticles, for the realization of wavelength sensitive ultra-minituarized (4×4 µm) optical metadevices. To this end the example of a 1.3/1.6 µm wavelength demultiplexer is considered. Its technological implementation is based on the integration of gold cut wire based metalines on the top of a silicon on insulator waveguide. The plasmonic metalines modify locally the effective index of the Si waveguide and thus allow for the implementation of wavelength dependent optical pathways. The 1.3/1.6µm wavelength separation with extinction ratio between two demultiplexer's channels reaching up to 20dB is experimentally demonstrated. The considered approach, which can be readily adapted to other planar lightwave circuits platforms and nanoresonators of different types of materials, is suited for the implementation of a generic family of wavelength sensitive guided wave optical metadevices. http://dx

Weblab France-Brésil en génie des procédés

A Weblab is an experiment remotely operated via internet. A Weblab between the Chemical Engineering Department of the University of São Paulo Polytechnic School (EPUSP) and the Process Engineering Department of the Ecole Nationale Supérieurs d’Ingénieurs en Arts Chimiques et Technologiques (ENSIACET) is developed. The experiment consists of a tank level control. The main objective is to propose and test tunings for the system control loop. For this purpose, the students must work in synergy and propose models for the system in order to find the tuning parameters. Weblab is a showcase for new technologies and original experiences because it allows to perform a control action from anywhere in a supervision environment which is spreading out in the industry. The objectives and interests are mainly pedagogical as the Weblab favours the variety and diversity of intercultural experiences a student could experience during his undergraduate studies. Because of this, the Weblab perfectly integrates in an engineer curriculum that is open to international exchanges. Un WebLab est une installation commandée à distance via internet. Nous développons une expérience de Weblab entre le département de Génie Chimique de l’Ecole Polytechnique de l’Université de São Paulo (EPUSP) et le département Génie des Procédés et Informatique de l’Ecole Nationale Supérieurs d’Ingénieurs en Arts Chimiques et Technologiques (ENSIACET). L’expérience consiste en la régulation de niveau dans un bac. L’objectif de l’expérience est de proposer et de valider des réglages pour la boucle de commande du système. Pour cela, les étudiants de l’EPUSP et de l’ENSIACET doivent travailler en synergie et proposer des modélisations et un réglage du contrôleur. Le Weblab constitue une vitrine de technologies innovantes et d’expériences originales, car il permet, depuis n’importe où, d’effectuer une commande à distance dans un environnement de supervision qui est de plus en plus adopté dans l’industrie. Les objectifs et intérêts du WebLab se situent plutôt au niveau pédagogique car il peut être un facteur multiplicatif du nombre d’expériences interculturelles pouvant être vécues par un étudiant tout au long de son cursus. Pour ces raisons le Weblab s’intègre parfaitement dans une formation d’ingénieurs qui se doit d’être ouverte à l’international