328 research outputs found

    Rare-earth-activated glasses for solar energy conversion

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    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

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    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

    NOD × 129.H2g7 Backcross Delineates 129S1/SvImJ-Derived Genomic Regions Modulating Type 1 Diabetes Development in Mice

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    OBJECTIVE: Introduction of genes targeted in 129/Sv embryonic stem (ES) cells into NOD mice brings about linked genes that may modulate type 1 diabetes. Our objective was to identify 129S1/SvJ non-MHC regions contributing type 1 diabetes resistance or susceptibility in backcross to NOD/LtJ. RESEARCH DESIGN AND METHODS: After congenic transfer of the NOD H2(g7) haplotype onto 129S1/Sv, 310 females were produced by NOD x (NOD x 129.H2(g7))F1 backcross (N2). A genome scan for quantitative trait locus (QTL) affecting clinical diabetes, age of diabetes onset, and insulitis severity was performed using subphenotype characteristics to improve power and resolution for detection of diabetes susceptibility loci. RESULTS: Thirty-six of 310 (11.6%) N2 females developed type 1 diabetes between 14 and 40 weeks. Significant evidence of linkage for only a single previously reported Idd complex locus (Idd10/17/18, chromosome [Chr] 3) was indicated for clinical diabetes. The quantitative traits of insulitis either alone or combined with age at type 1 diabetes onset were significantly linked to known Idd regions on Chr 1 (Idd5 region), Chr 4 (Idd9 region), Chr 8 (Idd22), Chr 11 (Idd4.3), and proximal Chr 17 (Idd16 region). Significant 129S1/Sv resistance contributions were identified on Chr 1, 15 (two loci), and 19, with suggestive evidence for additional novel 129/Sv resistance QTL on Chr 5 and 17 and susceptibility on Chr 2. CONCLUSIONS: The 129S1/SvJ genome harbors collections of both known and potentially novel non-MHC Idd loci. Investigators targeting 129/Sv genes mapping within chromosomal regions reported herein or elsewhere in the genome need to exclude potential contributions from linked Idd loci by generating a NOD.129 control strain expressing the nontargeted allele

    On the stability of peptide nucleic acid duplexes in the presence of organic solvents

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    Nucleic acid double helices are stabilized by hydrogen bonding and stacking forces (a combination of hydrophobic, dispersive and electrostatic forces) of the base pairs in the helix. One would predict the hydrogen bonding contributions to increase and the stacking contributions to decrease as the water activity in the medium decreases. Study of nucleobase paired duplexes in the absence of water and ultimately in pure aprotic, non-polar organic solvents is not possible with natural phosphodiester nucleic acids due to the ionic phosphate groups and the associated cations, but could be possible with non-ionic nucleic acid analogues or mimics such as peptide nucleic acids. We now report that peptide nucleic acid (PNA) (in contrast to DNA) duplexes show almost unaffected stability in up to 70% dimethylformamide (DMF) or dioxane, and extrapolation of the data to conditions of 100% organic solvents indicates only minor (or no) destabilization of the PNA duplexes. Our data indicate that stacking forces contribute little if at all to the duplex stability under these conditions. The differences in behaviour between the PNA and the DNA duplexes are attributed to the differences in hydration and counter ion release rather than to the differences in nucleobase interaction. These results support the possibility of having stable nucleobase paired double helices in organic solvents

    A Study of the Luminosity and Mass Functions of the Young IC 348 Cluster using FLAMINGOS Wide-Field Near-Infrared Images

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    We present wide-field near-infrared (JHK) images of the young, 2 Myr IC 348 cluster taken with FLAMINGOS. We use these new data to construct an infrared census of sources, which is sensitive enough to detect a 10 Mjup brown dwarf seen through an extinction of Av=7mag. We examine the cluster's structure and relationship to the molecular cloud and construct the cluster's K band luminosity function. Using our model luminosity function algorithm, we derive the cluster's initial mass function throughout the stellar and substellar regimes and find that the IC 348 IMF is very similar to that found for the Trapezium Cluster with both cluster IMFs having a mode between 0.2 - 0.08 Msun. In particular we find that, similar to our results for the Trapezium, brown dwarfs constitute only 1 in 4 of the sources in the IC 348 cluster. We show that a modest secondary peak forms in the substellar IC 348 KLF, corresponding to the same mass range responsible for a similar KLF peak found in the Trapezium. We interpret this KLF peak as either evidence for a corresponding secondary IMF peak at the deuterium burning limit, or as arising from a feature in the substellar mass-luminosity relation that is not predicted by current theoretical models. Lastly, we find that IC 348 displays radial variations of its sub-solar (0.5 - 0.08 Msun) IMF on a parsec scale. Whatever mechanism that is breaking the universality of the IMF on small spatial scales in IC 348 does not appear to be acting upon the brown dwarf population, whose relative size does not vary with distance from the cluster center.Comment: 53 pages, 20 figures, AASTeX5.0. Color version of Figure 1 made available in jpg format. Figure(s) 2,3,5 are reduced in resolution. Accepted 14 Jan 2003 to the Astronomical Journa

    International multicentre observational study to assess the efficacy and safety of a 0·5 mg kg−1 per day starting dose of oral corticosteroids to treat bullous pemphigoid

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    BackgroundEuropean guidelines propose a 0 center dot 5 mg kg(-1) per day dose of oral prednisone as initial treatment for bullous pemphigoid (BP). We assessed the safety and efficacy of this regimen depending on BP extent and general condition of the patients.MethodsIn a prospective international study, we consecutively included all patients diagnosed with BP. Patients received a 0 center dot 5 mg kg(-1) per day dose of prednisone, which was then gradually tapered 15 days after disease control, with the aim of stopping prednisone or maintaining minimal treatment (0 center dot 1 mg kg(-1) per day) within 6 months after the start of treatment. The two coprimary endpoints were control of disease activity at day 21 and 1-year overall survival. Disease severity was assessed according to the Bullous Pemphigoid Disease Area Index (BPDAI) score.ResultsIn total, 198 patients were included between 2015 and 2017. The final analysis comprised 190 patients with a mean age of 80 center dot 9 (SD 9 center dot 1) years. Control of disease activity was achieved at day 21 in 119 patients [62 center dot 6%, 95% confidence interval (CI) 55 center dot 3-69.5]; 18 of 24 patients (75%, 95% CI 53 center dot 3-90 center dot 2), 75 of 110 patients (68 center dot 8%, 95% CI 59 center dot 2-77 center dot 3) and 26 of 56 patients (46.4%, 95% CI 33 center dot 0-60 center dot 3) had mild, moderate and severe BP, respectively (P = 0 center dot 0218). A total of 30 patients died during the study. The overall Kaplan-Meier 1-year survival was 82 center dot 6% (95% CI 76 center dot 3-87 center dot 4) corresponding to 90 center dot 9%, 83 center dot 0% and 80 center dot 0% rates in patients with mild, moderate and severe BP, respectively (P = 0 center dot 5). Thresholds of 49 points for BPDAI score and 70 points for Karnofsky score yielded maximal Youden index values with respect to disease control at day 21 and 1-year survival, respectively.ConclusionsA 0 center dot 5 mg kg(-1) per day dose of prednisone is a valuable therapeutic option in patients with mild or moderate BP whose general condition allows them to be autonomous.</p

    Fe–FeO and Fe–Fe<sub>3</sub>C melting relations at Earth's core–mantle boundary conditions: Implications for a volatile-rich or oxygen-rich core

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    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

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    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
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