Molecular outflows in the young open cluster IC348

We present a wide-field survey of the young open cluster IC348 for molecular H2 outflows. Outflow activity is only found at its south-western limit, where a new subcluster of embedded sources is in an early phase of its formation. If the IC348 cluster had been built up by such subclusters forming at different times, this could explain the large age-spread that Herbig (1998) found for the IC348 member stars. In addition to several compact groups of H2 knots, our survey reveals a large north-south oriented outflow, and we identify the newly discovered far-infrared and mm-object IC348MMS as its source. New deep images in the 1-0 S(1) line of molecular hydrogen trace the HH211 jet and counterjet as highly-collimated chains of knots, resembling the interferometric CO and SiO jets. This jet system appears rotated counter-clockwise by about 3 degrees with respect to the prominent H2 bow shocks. Furthermore, we resolve HH211-mm as a double point-like source in the mm-continuum.Comment: 10 pages, 9 figures, accepted for publication in Ap

Rare-earth-activated glasses for solar energy conversion

The solar cells efficiency may be improved by better exploitation of the solar spectrum, making use of the down-conversion mechanism, where one high energy photon is cut into two low energy photons. The choice of the matrix is a crucial point to obtain an efficient down-conversion process with rare-earth ions. When energy transfer between rare earth ions is used to activate this process, high emission and absorption cross sections as well as low cut-off phonon energy are mandatory. In this paper we present some results concerning 70SiO2-30HfO2 glass ceramic planar waveguides co-activated by Tb3+/Yb3+ ions, fabricated by sol gel route using a top-down approach, and a bulk fluoride glass of molar composition 70ZrF4 23.5LaF3 0.5AlF3 6GaF3 co-activated by Pr3+/Yb3+ ion. Attention is focused on the assessment of the energy transfer efficiency between the two couples of rare earth ions in the different hosts

Experimental investigation of the stability of Fe-rich carbonates in the lower mantle

International audienceThe fate of carbonates in the Earth's mantle plays a key role in the geodynamical carbon cycle. Although iron is a major component of the Earth's lower mantle, the stability of Fe-bearing carbonates has rarely been studied. Here we present experimental results on the stability of Fe-rich carbonates at pressures ranging from 40 to 105 GPa and temperatures of 1450-3600 K, corresponding to depths within the Earth's lower mantle of about 1000-2400 km. Samples of iron oxides and iron-magnesium oxides were loaded into CO2 gas and laser heated in a diamond-anvil cell. The nature of crystalline run products was determined in situ by X-ray diffraction, and the recovered samples were studied by analytical transmission electron microscopy and scanning transmission X-ray microscopy. We show that Fe-(II) is systematically involved in redox reactions with CO2 yielding to Fe-(III)-bearing phases and diamonds. We also report a new Fe-(III)-bearing high-pressure phase resulting from the transformation of FeCO3 at pressures exceeding 40 GPa. The presence of both diamonds and an oxidized C-bearing phase suggests that oxidized and reduced forms of carbon might coexist in the deep mantle. Finally, the observed reactions potentially provide a new mechanism for diamond formation at great depth

The impact of ENSO on Southern African rainfall in CMIP5 ocean atmosphere coupled climate models

We study the ability of 24 ocean atmosphere global coupled models from the Coupled Model Intercomparison Project 5 (CMIP5) to reproduce the teleconnections between El Niño Southern Oscillation (ENSO) and Southern African rainfall in austral summer using historical forced simulations, with a focus on the atmospheric dynamic associated with El Niño. Overestimations of summer rainfall occur over Southern Africa in all CMIP5 models. Abnormal westward extensions of ENSO patterns are a common feature of all CMIP5 models, while the warming of the Indian Ocean that happens during El Niño is not correctly reproduced. This could impact the teleconnection between ENSO and Southern African rainfall which is represented with mixed success in CMIP5 models. Large-scale anomalies of suppressed deep-convection over the tropical maritime continent and enhanced convection from the central to eastern Pacific are correctly simulated. However, regional biases occur above Africa and the Indian Ocean, particularly in the position of the deep convection anomalies associated with El Niño, which can lead to the wrong sign in rainfall anomalies in the northwest part of South Africa. From the near-surface to mid-troposphere, CMIP5 models underestimate the observed anomalous pattern of pressure occurring over Southern Africa that leads to dry conditions during El Niño years

Studies on Pr3+–Yb3+ codoped ZBLA as rare earth down convertor glasses for solar cells encapsulation

The non-absorption of photons with energies below the bandgap (Eg) and the thermalization of photons with energies higher than Eg are the dominant loss processes of single-junction solar cells. Rare earth doped glasses give the opportunity to convert the incident photons wavelength and hence to increase or decrease their energies. The conversion of photons energies by “up or down conversion” leads to the possibility to increase the efficiencies of all classes of single-junction solar cells. Depending on the nature of doping materials, two low energy photons can be converted into one high-energy photon (up-conversion), or one high energy photon, can be converted into two low energy photons (down-conversion). In this paper, Pr3+–Yb3+ down-conversion co-doped ZBLA glasses were tested as encapsulation materials for silicon solar cells. The J–V characterizations were done under solar simulator irradiation. The influence of Yb3+ concentration on the solar cells performances was investigated, showing that an optimum value between 0.5 and 2 mol% conducts to an increase of the device efficiency comparing to mono-doped ZBLA material

Site selection spectroscopy in Eu3+-doped lanthanum fluorozirconate glass and glass-ceramic

The optical properties of Eu3+-doped glass and transparent glass-ceramic with composition (in mol%) 70.2ZrF4–23.4LaF3–0.6AlF3–5.8GaF3 were investigated by site selective spectroscopy in order to study the effect of ceramization on the symmetry of Eu3 + sites. The glass-ceramic obtained after thermal treatment of the glass ZLAG contains a unique crystalline phase of unknown structure. The analysis and comparison of FLN spectra in these materials are presented and different classes of sites are discussed. We found the presence of two main site distributions for Eu3+ ions of equivalent symmetry (C2v or lower) in the glass and two sites of different symmetry (C2v or lower and C4v or lower) in tthe glass-ceramic (GC). The estimated average crystal field strength for glass and GC decreases with the 5D0 → 7F0 energy. The results suggest that the two kinds of sites identified in the glass correspond to Eu3+ ions in and out of the former network. Decay-time measurements of 5D0 level of Eu3 + evidenced energy transfer between high and low energy sites and showed an increase of lifetime from the glass to the glass-ceramic

Fe–FeO and Fe–Fe₃C melting relations at Earth's core–mantle boundary conditions: Implications for a volatile-rich or oxygen-rich core

International audienceEutectic melting temperatures in the Fe–FeO and Fe–Fe3C systems have been determined up to 150 GPa. Melting criteria include observation of a diffuse scattering signal by in situ X-Ray diffraction, and textural characterisation of recovered samples. In addition, compositions of eutectic liquids have been established by combining in situ Rietveld analyses with ex situ chemical analyses. Gathering these new results together with previous reports on Fe–S and Fe–Si systems allow us to discuss the specific effect of each light element (Si, S, O, C) on the melting properties of the outer core. Crystallization temperatures of Si-rich core compositional models are too high to be compatible with the absence of extensive mantle melting at the core–mantle boundary (CMB) and significant amounts of volatile elements such as S and/or C (>5 at%, corresponding to >2 wt%), or a large amount of O (>15 at% corresponding to ∼5 wt%) are required to reduce the crystallisation temperature of the core material below that of a peridotitic lower mantle

Structure and density of Fe-C liquid alloys under high pressure

International audienceThe density and structure of liquid Fe-C alloys have been measured up to 58 GPa and 3,200 K by in situ X-ray diffraction using a Paris-Edinburgh press and laser-heated diamond anvil cell. Study of the pressure evolution of the local structure inferred by X-ray diffraction measurements is important to understand the compression mechanism of the liquid. Obtained data show that the degree of compression is greater for the first coordination sphere than the second and third coordination spheres. The extrapolation of the measured density suggests that carbon cannot be the only light element alloyed to iron in the Earth's core, as 8-16 at % C (1.8-3.7 wt % C) would be necessary to explain the density deficit of the outer core relative to pure Fe. This concentration is too high to account for outer core velocity. The presence of other light elements (e.g., O, Si, S, and H) is thus required