Effet de la température sur l'installation et la croissance des plantes annuelles de marais temporaires méditerranéens

L'abondance des plantes annuelles des marais temporaires est soumise à de fortes fluctuations dans le temps. Celles-ci peuvent être dues à la variabilité du climat méditerranéen. Nous avons étudié expérimentalement la relation entre ces variations d'abondance et la température de l'eau. La phase d'installation et la phase de croissance des espèces ont été étudiées dans trois gammes de températures. Chaque espèce possède son propre patron de germination, lequel varie avec la température. La vitesse d'émergence des plantules de toutes les espèces change en relation avec la température. Le taux de germination n'est modifié significativement que pour les charophytes, avec une forte diminution en conditions froides. L'abondance des réserves de semences de #Chara sp. et de #Zannichellia spp. explique en grande partie leur dynamique de germination. Le recouvrement à la fin de la phase d'installation est maximal en conditions chaudes et le #Callitriche truncata et les #Zannichellia spp. présentent plus fortes valeurs. En fin de période de croissance, le #Ranunculus baudotii domine généralement la communauté en terme de biomasse tandis que le #C. truncata est dominé. La biomasse des espèces est modifiée par la température de la phase d'installation et (ou) de croissance, sauf pour les #Zannichellia$ spp. Il n'existe pas d'effet de "préemption" apparent : les stratégies de vie contrastées des espèces aboutissent à modifier les relations de dominance au cours du cycle de vie. (Résumé d'auteur

Basic studies on dispersion hardening

Transmission electron microscopy and X-ray diffraction observations of substructure and elastic strains in cold worked and annealed dispersion strengthened alloy

Effect of a Grazing Intensity Gradient on Primary Production and Soil Nitrogen Mineralisation in a Humid Grassland of Western France

Large herbivores have a major influence on the structure and the functions of humid grasslands and especially on primary production. Earlier work on the study site showed that grazing intensity was spatially varied and created a diversity of vegetation patches in the grassland (Loucougaray, 2003). The first objective of this study was to determine whether the variation in grazing intensity led to variation of primary production within the three plant communities located at three topographic levels in the grassland. The second objective was to determine whether a relationship linked primary production variation and net soil nitrogen (N) mineralisation

Per una ricapitalizzazione efficacenete co-creativa dei sistemi territoriali italiani

La trasformazione creativa (innovazione) non dovrebbe essere immaginata se non come emergente dall’interazione interna (immanente) ai soggetti individuali o inter-individuali, piuttosto che da istanze separate e superiori (trascendenti). Il compito del planning dovrebbe quindi essere quello di rendere percepibili le potenzialità di cambiamento emergenti dall’interazione della molteplicità di detentori di quote di capitale urbano (stakeholder), che includono in pratica la totalità dei soggetti, e di fornire loro validi framework di orientamento e di scambio tra differenti, e spesso inconciliabili, sistemi di ‘valori’. Sono insomma richiesti approcci innovativi all’‘urbano’, per lo più contrastanti con le tradizionali prassi di investimento infrastrutturale, realizzate a scapito dell’investimento in ‘capitale umano’. Per superare la vieta dicotomia tra approcci top-down e bottom-up appare inoltro opportuno far riferimento a un nuovo modello di governance caratterizzato da reti auto-organizzate assimilabili a un fenomeno spontaneo guidato da processi sociali più che da obiettivi politici. A questo modello social di governance fanno riferimento i cosiddetti Living Lab urbani e territoriali, da considerare come veri e propri ecosistemi di agenzie che, interagendo co-creativamente, sembrano poter costituire un utile riferimento per l’integrazione multi scalare dei livelli di governo e che, attraverso la condivisione di un’idea di impresa e/o di una problematica, sembrano anche in grado di produrre concreti effetti di rigenerazione urbano-territoriale

Ultrasensitive Displacement Noise Measurement of Carbon Nanotube Mechanical Resonators

Mechanical resonators based on a single carbon nanotube are exceptional sensors of mass and force. The force sensitivity in these ultra-light resonators is often limited by the noise in the detection of the vibrations. Here, we report on an ultra-sensitive scheme based on a RLC resonator and a low-temperature amplifier to detect nanotube vibrations. We also show a new fabrication process of electromechanical nanotube resonators to reduce the separation between the suspended nanotube and the gate electrode down to $\sim 150$~nm. These advances in detection and fabrication allow us to reach $0.5~\mathrm{pm}/\sqrt{\mathrm{Hz}}$ displacement sensitivity. Thermal vibrations cooled cryogenically at 300~mK are detected with a signal-to-noise ratio as high as 17~dB. We demonstrate $4.3~\mathrm{zN}/\sqrt{\mathrm{Hz}}$ force sensitivity, which is the best force sensitivity achieved thus far with a mechanical resonator. Our work is an important step towards imaging individual nuclear spins and studying the coupling between mechanical vibrations and electrons in different quantum electron transport regimes.Comment: 9 pages, 5 figure

Superselectors: Efficient Constructions and Applications

We introduce a new combinatorial structure: the superselector. We show that superselectors subsume several important combinatorial structures used in the past few years to solve problems in group testing, compressed sensing, multi-channel conflict resolution and data security. We prove close upper and lower bounds on the size of superselectors and we provide efficient algorithms for their constructions. Albeit our bounds are very general, when they are instantiated on the combinatorial structures that are particular cases of superselectors (e.g., (p,k,n)-selectors, (d,\ell)-list-disjunct matrices, MUT_k(r)-families, FUT(k, a)-families, etc.) they match the best known bounds in terms of size of the structures (the relevant parameter in the applications). For appropriate values of parameters, our results also provide the first efficient deterministic algorithms for the construction of such structures

Imaging striatal dopamine release using a nongenetically encoded near infrared fluorescent catecholamine nanosensor.

Neuromodulation plays a critical role in brain function in both health and disease, and new tools that capture neuromodulation with high spatial and temporal resolution are needed. Here, we introduce a synthetic catecholamine nanosensor with fluorescent emission in the near infrared range (1000-1300 nm), near infrared catecholamine nanosensor (nIRCat). We demonstrate that nIRCats can be used to measure electrically and optogenetically evoked dopamine release in brain tissue, revealing hotspots with a median size of 2 µm. We also demonstrated that nIRCats are compatible with dopamine pharmacology and show D2 autoreceptor modulation of evoked dopamine release, which varied as a function of initial release magnitude at different hotspots. Together, our data demonstrate that nIRCats and other nanosensors of this class can serve as versatile synthetic optical tools to monitor neuromodulatory neurotransmitter release with high spatial resolution

pH prediction in concentrated aqueous solutions under high pressure of acid gases and high temperature

International audienceAn extended model for pH prediction in oil and gas environments has been developed. Accurate pH calculations for high pressure and high temperature applications depends mainly on CO2 and H2S partial pressures, the ionic strength, the chemical composition of the solution, and the temperature. Accounting for the non-ideal behaviors of liquid and gas phases allows pH calculations up to 200 °C, 2000 bar total pressure, and ionic strengths up to 5 mol.L-1. The results are consistent with experimental measurements and with other models reported in the literature

Improving pH Prediction for High Pressure and High Temperature Applications in Oil and Gas Production

International audiencepH prediction represents a crucial step before selecting materials for use in sour oil and gas wells as regards weight loss corrosion and H 2 S cracking. Among the numerous parameters which determine the equilibrium pH, important ones are CO 2 and H 2 S partial pressures (P CO2 and P H2S respectively), the total pressure, the ionic strength and the chemical composition of the solution, and the temperature. Most models used by oil and gas operators present a too narrow range of validity for these parameters, which makes them inappropriate for high pressure and high temperature (HPHT) fields or for CO 2 reinjection. This paper presents modeling improvements which allows extending the prediction validity in temperature and pressure to respectively 200 °C and 1,000 bar of total pressure, and for an ionic strength up to 5 mol.kg-1. These improvements take into account the fugacities in gas phase of CO 2 and H 2 S as determined by the Soreide and Whitson formalism. The influence of water and CH 4 pressure is also taken into account up to several hundred bars. Activity coefficients in the water phase are calculated using the Pitzer model. The consistency of the model is verified by comparison with experimental measurements of pH under high pressure. It is then applied to oil and gas applications at high pressure and high temperature. The impact of the new calculation method is discussed both for pH evaluation and also for H 2 S activity, with strong implications for the evaluation of SSC risks

Patients' use of a home-based virtual reality system to provide rehabilitation of the upper limb following stroke

Background: A low cost, virtual reality system that translates movements of the hand, fingers and thumb into game play was designed to provide a flexible and motivating approach to increasing adherence to home based rehabilitation. Objective: Effectiveness depends on adherence, so did patients use the intervention to the recommended level. If not, what reasons did they give? Design: Prospective cohort study plus qualitative analysis of interviews. Methods: 17 patients recovering from stroke recruited to the intervention arm of a feasibility trial had the equipment left in their homes for eight weeks and were advised to use it three times a day for periods of no more than 20 minutes. Frequency and duration of use were automatically recorded. At the end of the intervention, participants were interviewed to determine barriers to using it in the recommended way. Results: Duration of use and how many days they used the equipment are presented for the 13 participants who successfully started the intervention. These figures were highly variable and could fall far short of our recommendations. There was a weak (p=0.053) positive correlation between duration and baseline reported activities of daily living. Participants reported familiarity with technology and competing commitments as barriers to use although appreciated the flexibility of the intervention and found it motivating