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9,9'-Spirobifluorene and 4-phenyl-9,9'- spirobifluorene: pure hydrocarbon small molecules as hosts for efficient green and blue PhOLEDs
No full textInternational audienceWe report herein a new pure hydrocarbon material, 4-phenyl-9,9′-spirobifluorene (4-Ph-SBF), with a high triplet energy level (ET: 2.77 eV) as a host for blue phosphorescent organic light-emitting diodes (PhOLEDs). Structural, thermal, electrochemical and photophysical properties have been investigated in detail and compared to its constituting building block 9,9′-spirobifluorene (SBF) in order to precisely study the influence of the incorporation of a phenyl unit in C4. A surprising out of plane deformation of the fluorene ring and a highly twisted structure have been notably found for 4-Ph-SBF due to the substitution in C4. As both 4-Ph-SBF and SBF possess a high triplet energy level (2.77/2.87 eV resp.), they have been successfully used as host materials for green and blue PhOLEDs. The performance of blue PhOLEDs, ca. 20 cd A−1, appears to be among the highest reported for pure hydrocarbon derivatives
Objets non mouillants : de l'impact à l'autopropulsion
No full textWe investigate through several experiments the special dynamics generated by non-wetting objects.On a substrate textured with grooves forming a herringbone pattern, a Leidenfrost levitating liquid is propelled: the textures channel the vapor flow in a well-defined direction so that the slider above is driven by vapor viscosity. These deformable objects undergo very little friction on flat surfaces. However, on crenelated substrates, impacts on the texture sides greatly enhance dissipation. We extend this entrainment scenario to other situations where the liquid (and its deformable nature) is not involved anymore. A solid plate can levitate over a porous substrate through which air is blown. Again, escaping flow can be rectified by the textures and entrain the plate, leading to translation movement or even to rotation. If we create deeper channels (hence losing flow confinement), we observe motion in the opposite direction due to “rocket effect” (conservation of momentum). We are also interested in an extreme non-wetting situation: the falling drop. Indeed, all along the fall, the drop only experiences air drag friction, easily reaching high speeds. We tackle the problem of the dramatic issue of this fall: the impact. We first study the impact of a drop on a sieve. In this situation intermediate between a solid wall and no obstacle at all, mass either passes through the holes or gets stopped by the closings. We then focus on the impact force experienced by the substrates and characterize the force as a function of the drop and impact properties, but also of the nature of the solid on which impact takes place.Nous étudions à travers plusieurs expériences la dynamique spéciale engendrée par des objets non mouillants. Un liquide en état Leidenfrost est autopropulsé lorsqu’on le pose sur un substrat texturé avec des rainures formant un motif à chevrons: les textures canalisent l'écoulement de vapeur dans une direction bien définie de sorte que ces aéroglisseurs liquides sont entraînés par la vapeur sous-jacente. Ces objets déformables subissent très peu de friction sur une surface plane. Toutefois, sur des substrats crénelés, les impacts sur les textures créent une friction spéciale qui est également étudiée. Nous étendons ce scénario d'entraînement visqueux dans d'autres situations où le liquide est remplacé par une plaque solide. Pour permettre la lévitation, on le place sur un substrat poreux à travers lequel de l'air est soufflé. Une fois de plus, l’écoulement est rectifié par des textures permettant l’entraînement d’une lamelle de verre dans un mouvement de translation ou même de rotation. Si nous augmentons la profondeur des textures, le confinement est perdu et on observe un mouvement dans la direction opposée dû à l'effet fusée. Nous nous intéressons également à une situation de non mouillage particulièrement simple: la goutte en chute libre. Nous abordons le problème de l’issue de cette chute: l'impact. Nous étudions d'abord l'impact d'une goutte sur un tamis. Dans cette situation, le liquide passe à travers les trous ou est arrêté par les sections bouchées. Nous nous concentrons ensuite à la force d’impact subie par le substrat. Nous la mesurons et la calculons en fonction des caractéristiques du liquide, de l’impact, et de la nature du substrat
Coupling CALIOP observations and regional simulations at 20km resolution: is that a good candidate to study cloud variability at the regional scale?
No full textInternational audienceThis work aims to study the clouds' role on regional climate variability. At first order, European climate is driven by large scale circulations. However, clouds are known to have two major radiative effects impacting the surface temperature: the greenhouse effect and the albedo effect. These effects are strongly dependent on macrophysical and microphysical properties of clouds. It is then necessary to consider the vertical distribution of clouds to better understand their impact on regional climate. Since June 2006, A-train observations are available and allow the description of this vertical distribution and of other microphysical properties. However, the sampling is limited when considering small scale variability. To complete these observations, we use a regional climate model which may allow to extend the period of study and to better understand the link between clouds and surface temperature. In this study we address the ability of our tools to study impact of clouds on European climate at a resolution suitable to take into account the complex terrain of this area. Seasonal and inter annual clouds variability is presented for observations and simulations. We also evaluate the amplitude of clouds variability in the simulations and the uncertainties linked to the satellite sampling. B. Effect of satellite under sampling GCM Oriented Calipso Cloud Product-GOCCP (Chepfer et al., 2010) Using the microphysical properties of the simulated clouds, we compute the SR that would be observed by the CALIOP lidar. We can then use the same cloud diagnostics for both observations and simulations WRF-MedCordex simulations Adaptation of COSP Lidar Simulator 2 GOCCP products have been used for this study: o Scattering Ratio: SR = í µí°´í µí±í µí°µ í µí±¡í µí±í µí±¡ í µí°´í µí±í µí°µ í µí±í µí±í µí± o Cloud fraction (z) : % of SR>5 on 20km grid (tab. 1) Altitude (km) altitude latitude Fig3: Instant SR 19/01/2009 night: (a) Observations, (b) WRF simulations and (c) WRF+lidar simulator simulations We use a WRF simulation performed in the framework of MED-CORDEX (downscaling of ERA-interim reanalyses) at 20 km resolution that covers the Mediterranean domain, over the period 1989-2011 (details in Stefanon et al., 2014).-horizontal resolution: 20km-28 vertical levels, outputs every 3 hours o Very similar profiles of cloud fraction (CF) o High clouds (10 km): in average, differences need to compute CF from mixing ratio
Public transport reliability and commuter strategy
No full textThis is the accepted version of a paper published as: Monchambert, G., & De Palma, A. (2014). Public transport reliability and commuter strategy. Journal of Urban Economics, 81, 14-29.This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. Access to the published version may require subscription.N.B. When citing this work, cite the original published paperInternational audienceWe consider the modeling of a bi-modal competitive network involving a public transport mode, which may be unreliable, and an alternative mode. Commuters select a transport mode and their arrival time at the station when they use public transport. The public transport reliability set by the public transport firm at the competitive equilibrium increases with the alternative mode fare, via a demand effect. This is reminiscent of the Mohring effect. The study of the optimal service quality shows that often, public transport reliability and thereby patronage are lower at equilibrium compared to first-best social optimum. The paper provides some public policy insights
Assessment for Decision-Makers Scientiic Assessment of Ozone Depletion: 2014 World Meteorological Organization United Nations Environment Programme National Oceanic and Atmospheric Administration National Aeronautics and Space Administration European Commission
No full textActions taken under the Montreal Protocol have led to decreases in the atmospheric abundance of controlledozone-depleting substances (ODSs), and are enabling the return of the ozone layer toward 1980 levels.• The sum of the measured tropospheric abundances of substances controlled under the MontrealProtocol continues to decrease. Most of the major controlled ODSs are decreasing largely as projected, andhydrochlorofluorocarbons (HCFCs) and halon-1301 are still increasing. Unknown or unreported sources of carbontetrachloride are needed to explain its abundance.• Measured stratospheric abundances of chlorine- and bromine-containing substances originating from thedegradation of ODSs are decreasing. By 2012, combined chlorine and bromine levels (as estimated by EquivalentEffective Stratospheric Chlorine, EESC) had declined by about 10–15% from the peak values of ten to fifteen years ago.Decreases in atmospheric abundances of methyl chloroform (CH3CCl3), methyl bromide (CH3Br), and chlorofluorocarbons(CFCs) contributed approximately equally to these reductions.• Total column ozone declined over most of the globe during the 1980s and early 1990s (by about 2.5% averagedover 60°S to 60°N). It has remained relatively unchanged since 2000, with indications of a small increase in totalcolumn ozone in recent years, as expected. In the upper stratosphere there is a clear recent ozone increase, whichclimate models suggest can be explained by comparable contributions from declining ODS abundances and upperstratospheric cooling caused by carbon dioxide increases.• The Antarctic ozone hole continues to occur each spring, as expected for the current ODS abundances. The Arcticstratosphere in winter/spring 2011 was particularly cold, which led to large ozone depletion as expected under theseconditions.• Total column ozone will recover toward the 1980 benchmark levels over most of the globe under full compliancewith the Montreal Protocol. This recovery is expected to occur before midcentury in midlatitudes and the Arctic, andsomewhat later for the Antarctic ozone hole.The Antarctic ozone hole has caused significant changes in Southern Hemispheresurface climate in the summer.• Antarctic lower stratospheric cooling due to ozone depletion is very likely the dominant cause of observedchanges in Southern Hemisphere tropospheric summertime circulation over recent decades, with associatedimpacts on surface temperature, precipitation, and the oceans. In the Northern Hemisphere, no robust link has beenfound between stratospheric ozone depletion and tropospheric climate.Changes in CO2 , N2O, and CH4 will have an increasing influence on the ozone layer as ODSs decline.• As controlled ozone-depleting substances decline, the evolution of the ozone layer in the second half of the21st century will largely depend on the atmospheric abundances of CO2, N2O, and CH4. Overall, increasing carbondioxide (CO2 ) and methane (CH4 ) elevate global ozone, while increasing nitrous oxide (N2O) further depletes globalozone. The Antarctic ozone hole is less sensitive to CO2, N2O, and CH4 abundances.• In the tropics, significant decreases in column ozone are projected during the 21st century. Tropical ozone levelsare only weakly affected by ODS decline; they are sensitive to circulation changes driven by CO2 , N2O, and CH4 increases.The climate benefits of the Montreal Protocol could be significantly offset by projectedemissions of HFCs used to replace ODSs.The Montreal Protocol and its Amendments and adjustments have made large contributions toward reducing global greenhouse gasemissions. In 2010, the decrease of annual ODS emissions under the Montreal Protocol is estimated to be about 10 gigatonnes of avoidedCO2-equivalent emissions per year, which is about five times larger than the annual emissions reduction target for the first commitmentperiod (2008–2012) of the Kyoto Protocol (from the Executive Summary of the Scientific Assessment of Ozone Depletion: 2010).11 GWP-weighted emissions, also known as CO2-equivalent emissions, are defined as the amount of gas emitted multiplied by its 100-year Global WarmingPotential (GWP). Part of the effect of ODSs as greenhouse gases is offset by the cooling due to changes in ozone.Executive SummaryES-2• The sum of the hydrofluorocarbons (HFCs) currently used as ODS replacements makes a small contribution of about 0.5gigatonnes CO2-equivalent emissions per year. These emissions are currently growing at a rate of about 7% per year andare projected to continue to grow.• If the current mix of these substances is unchanged, increasing demand could result in HFC emissions of up to 8.8gigatonnes CO2-equivalent per year by 2050, nearly as high as the peak emission of CFCs of about 9.5 gigatonnes CO2-equivalent per year in the late 1980s.2• Replacements of the current mix of high-Global Warming Potential (GWP) HFCs with low-GWP compounds or not-inkindtechnologies would essentially avoid these CO2-equivalent emissions.• Some of these candidate low-GWP compounds are hydrofluoro-olefins (HFOs), one of which (HFO-1234yf) yields thepersistent degradation product trifluoroacetic acid (TFA) upon atmospheric oxidation. While the environmental effectsof TFA are considered to be negligible over the next few decades, potential longer-term impacts could require futureevaluations due to the environmental persistence of TFA and uncertainty in future uses of HFOs.• By 2050, HFC banks are estimated to grow to as much as 65 gigatonnes CO2-equivalent. The climate change impact ofthe HFC banks could be reduced by limiting future use of high-GWP HFCs to avoid the accumulation of the bank, or bydestruction of the banks.Additional important issues relevant to the Parties to the Montreal Protocol and otherdecision-makers have been assessed.• Derived emissions of carbon tetrachloride (CCl4), based on its estimated lifetime and its accurately measured atmosphericabundances, have become much larger than those from reported production and usage over the last decade.• As of 2009, the controlled consumption of methyl bromide declined below the reported consumption for quarantineand pre-shipment (QPS) uses, which are not controlled by the Montreal Protocol.• Increased anthropogenic emissions of very short-lived substances (VSLS) containing chlorine and bromine, particularlyfrom tropical sources, are an emerging issue for stratospheric ozone. The relative contribution of these emissions couldbecome important as levels of ODSs controlled under the Montreal Protocol decline.• As the atmospheric abundances of ODSs continue to decrease over the coming decades, N2O, as the primary source ofnitrogen oxides in the stratosphere, will become more important in future ozone depletion.• Emissions of HFC-23, a by-product of HCFC-22 production, have continued despite mitigation efforts.• While ODS levels remain high, a large stratospheric sulfuric aerosol enhancement due to a major volcanic eruption orgeoengineering activities would result in a substantial chemical depletion of ozone over much of the globe.While past actions taken under the Montreal Protocol have substantially reduced ODS production andconsumption, additional, but limited, options are available to reduce future ozone depletion.Emissions from the current banks are projected to contribute more to future ozone depletion than those caused by future ODS production,assuming compliance with the Protocol.• Possible options to advance the return of the ozone layerto the 1980 level (analyses based on midlatitude EESC) areshown graphically. The cumulative effect of eliminationof emissions from all banks and production advances thisreturn by 11 years.Scientific Steering Committee : Ayité-Lô Nohende AjavonDavid J. KarolyMalcolm K. KoPaul A. NewmanJohn A. PyleA.R. RavishankaraTheodore G. ShepherdSusan SolomonCoordinating EditorChristine A. Enni
Strain-induced inverse magnetostriction measured on a single contacted Ni nanowire in a polymer matrix Strain-induced inverse magnetostriction measured on a single contacted Ni nanowire in a polymer matrix
No full textInternational audienceThe effects of the thermoelastic and piezoelectric strain exerted by an active polymer matrix on a Ni nanowire (NW) are studied at the nanoscale by measuring the inverse magnetostriction of single-contacted Ni NWs. The reorientation of the magnetization is measured by anisotropic magnetoresitance. In the absence of strain, the Ni NW exhibits a typical uniform rotation of the magnetization as a function of the external field. When piezoelectric or ther-moelelastic strain is present in the polymer matrix, the hysteresis loop becomes strongly modified by the inverse magnetostriction of Ni. It is shown that the ferromagnetic NW plays then the role of a mechanical probe that allows the effects of the mechanical strain to be characterized and described qualitatively and quantitatively. Moreover the stress exerted by the polycarbonate matrix on the NW is found to be isotropic while the one produced by the PVDF matrix is anisotropic
Gold-Catalyzed Synthesis of Functionalized Pyridines by Using 2H-Azirines as Synthetic Equivalents of Alkenyl Nitrenes.
No full textInternational audience2H-Azirines are easily synthesized from the corresponding ketones and, despite possessing a CN bond embedded in a strained three-membered cycle, they are sufficiently stable to be isolated, stored, and manipulated. 2H-Azirines can be regarded as valuable synthetic equivalents of alkenyl nitrenes, however, reactions capitalizing on the cyclic strain of the heterocyclic motif and involving the cleavage of the CN single bond remain surprisingly limited. A gold-catalyzed reaction that allows the formation of polysubstituted functionalized pyridines from easily accessible 2-propargyl 2H-azirine derivatives was developed. This transformation, which corresponds to an unprecedented intramolecular transfer of an alkenyl nitrene to an alkyne, proceeds with low catalyst loading, is efficient, and exhibits a high functional-group tolerance and a wide substrate scope
Determination of collagen fiber orientation in histological slides using Mueller microscopy and validation by second harmonic generation imaging.
No full textInternational audienceWe studied the azimuthal orientations of collagen fibers in histological slides of uterine cervical tissue by two different microscopy techniques, namely Mueller polarimetry (MP) and Second Harmonic Generation (SHG). SHG provides direct visualization of the fibers with high specificity, which orientations is then obtained by suitable image processing. MP provides images of retardation (among other polarimetric parameters) due to the optical anisotropy of the fibers, which is enhanced by Picrosirius Red staining. The fiber orientations are then assumed to be those of the retardation slow axes. The two methods, though fully different from each other, provide quite similar maps of average fiber orientations. Overall, our results confirm that MP microscopy provides reliable images of dominant fiber orientations at a much lower cost that SHG, which remains the "gold standard" for specific imaging of collagen fibers using optical microscopy
Blow up for the critical gKdV equation I: dynamics near the soliton
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