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We report the use of DOTA as a chelator for titanium. The resulting complex is fully characterised and in vitro stability studies reveal its high kinetic inertness against transmetallation and transchelation. The radiolabeling of DOTA with 45Ti, via a guaiacol-based liquid–liquid extraction method, leads to a high radiochemical conversion up to 98%. [ABSTRACT FROM AUTHOR]

Following the projected increase in extreme precipitation, an increase in extreme snowfall may be expected in cold regions, e.g., for high latitudes or at high elevations. By contrast, in low- to medium-elevation areas, the probability of experiencing rainfall instead of snowfall is generally projected to increase due to warming conditions. Yet, in mountainous areas, despite the likely existence of these contrasted trends according to elevation, changes in extreme snowfall with warming remain poorly quantified. This paper assesses projected changes in heavy and extreme snowfall, i.e., in mean annual maxima and 100-year return levels, in the French Alps as a function of elevation and global warming level. We apply a recent methodology, based on the analysis of annual maxima with non-stationary extreme value models, to an ensemble of 20 adjusted general circulation model–regional climate model (GCM–RCM) pairs from the EURO-CORDEX experiment under the Representative Concentration Pathway 8.5 (RCP8.5) scenario. For each of the 23 massifs of the French Alps, maxima in the hydrological sense (1 August to 31 July) are provided from 1951 to 2100 and every 300 m of elevations between 900 and 3600 m. Results rely on relative or absolute changes computed with respect to current climate conditions (corresponding here to +1 ∘ C global warming level) at the massif scale and averaged over all massifs. Overall, daily mean annual maxima of snowfall are projected to decrease below 3000 m and increase above 3600 m, while 100-year return levels are projected to decrease below 2400 m and increase above 3300 m. At elevations in between, values are on average projected to increase until +3 ∘ C of global warming and then decrease. At +4 ∘ C, average relative changes in mean annual maxima and 100-year return levels, respectively, vary from -26% and -15% at 900 m to +3% and +8% at 3600 m. Finally, for each global warming level between +1.5 and +4 ∘ C, we compute the elevation threshold that separates contrasted trends, i.e., where the average relative change equals zero. This elevation threshold is shown to be lower for higher return periods, and it is projected to rise from 3000 m at +1.5 ∘ C to 3350 m at +4 ∘ C for mean annual maxima and from 2600 to 3000 m for 100-year return levels. These results have implications for the management of risks related to extreme snowfall. [ABSTRACT FROM AUTHOR]

Anticipating risks related to climate extremes often relies on the quantification of large return levels (values exceeded with small probability) from climate projection ensembles. Current approaches based on multi-model ensembles (MMEs) usually estimate return levels separately for each chain of the MME. By contrast, using MME obtained with different combinations of general circulation model (GCM) and regional climate model (RCM), our approach estimates return levels together from the past observations and all GCM-RCM pairs, considering both historical and future periods. The proposed methodology seeks to provide estimates of projected return levels accounting for the variability of individual GCM-RCM trajectories, with a robust quantification of uncertainties. To this aim, we introduce a flexible non-stationary generalized extreme value (GEV) distribution that includes i) piecewise linear functions to model the changes in the three GEV parameters ii) adjustment coefficients for the location and scale parameters to adjust the GEV distributions of the GCM-RCM pairs with respect to the GEV distribution of the past observations. Our application focuses on snow load at 1500m elevation for the 23 massifs of the French Alps, which is of major interest for the structural design of roofs. Annual maxima are available for 20 adjusted GCM-RCM pairs from the EURO-CORDEX experiment, under the scenario RCP8.5. Our results show with a model-as-truth experiment that at least two linear pieces should be considered for the piecewise linear functions. We also show, with a split-sample experiment, that eight massifs should consider adjustment coefficients. These two experiments help us select the GEV parameterizations for each massif. Finally, using these selected parameterizations, we find that the 50-year return level of snow load is projected to decrease in all massifs, by -2.9kNm-2 (-50%) on average between 1986-2005 and 2080-2099 at 1500m elevation and RCP8.5. This paper extends to climate extremes the recent idea to constrain climate projection ensembles using past observations. [ABSTRACT FROM AUTHOR]

In a context of climate change, trends in extreme snow loads need to be determined to minimize the risk of structure collapse. We study trends in annual maxima of ground snow load (GSL) using non-stationary extreme value models. Trends in return levels of GSL are assessed at a mountain massif scale from GSL data, provided for the French Alps from 1959 to 2019 by a meteorological reanalysis and a snowpack model. Our results indicate a temporal decrease in 50-year return levels from 900 m to 4200 m, significant in the Northwest of the French Alps until 2100 m. Despite this decrease, in half of the massifs, the return level in 2019 at 1800 m exceeds the return level designed for French building standards under a stationary assumption. We believe that this high number of exceedances is due to questionable assumptions concerning the computation of current standards. For example, these were devised with GSL, estimated from snow depth and constant snow density set to 150 kg m-3, which underestimate typical GSL values for the full snowpack. [ABSTRACT FROM AUTHOR]

Homoleptic rare-earth metal silylamide complexes Ln[[N[(Si[Me.sub.3]).sub.2]].sub.3] (Ln = Y, La, Nd) are grafted onto a series of partially dehydroxylated periodic mesoporous silica (PMS) supports. The studies have shown that under the prevailing slutty conditions the metal size, the pore size and the particle morphology have affected the catalytic performance.

A combination of experimental data and density functional theory calculations are used to study the nature and structure of alumina single site catalysts. The grafting mechanisms for these complexes on alumina are compared and are focused on the existence of cationic metallic species and on the unique character of the formed surface entity.

Kinetic studies on propane metathesis, in a continous flow reactor, have allowed primary products to be detected, namely olefins and H2. A mechanism is proposed on the basis of known elementary steps of organometallic chemistry, which is in full agreement with all the observed selectivities.

A series of hafnium complexes were structurally identified showing high activity (up to 500 h−1) in the selective alternated copolymerization of epoxides with CO2 under low pressure. [ABSTRACT FROM AUTHOR]