Gamma radiolytic stability of CyMe4BTBP and the effect of nitric acid

The highly selective nitrogen donor ligand CyMe4BTBP for An(III) separation by solvent extraction was irradiated in a 60Co γ-source under varying conditions. Organic solutions of 10 mmol/L ligand in 1-octanol were contacted with different concentrations of nitric acid to observe the influence of an aqueous phase during irradiation. In subsequent liquid-liquid extraction experiments, distribution ratios of 241Am and 152Eu were determined. Distribution ratios decreased with increasing absorbed dose when irradiation was performed in the absence of nitric acid. With addition of nitric acid, initial distribution ratios remained constant over the whole examined dose range up to 300 kGy. For qualitative determination of radiolysis products, HPLC-MS measurements were performed. The protective effect of nitric acid was confirmed, since in samples irradiated with acid contact, no degradation products were observed, but only addition products of the 1-octanol molecule to the CyMe4BTBP molecule

Gamma radiolytic stability of CyMe4BTBP and the effect of nitric acid

The highly selective nitrogen donor ligand CyMe4BTBP for An(III) separation by solvent extraction was irradiated in a 60Co γ-source under varying conditions. Organic solutions of 10 mmol/L ligand in 1-octanol were contacted with different concentrations of nitric acid to observe the influence of an aqueous phase during irradiation. In subsequent liquid-liquid extraction experiments, distribution ratios of 241Am and 152Eu were determined. Distribution ratios decreased with increasing absorbed dose when irradiation was performed in the absence of nitric acid. With addition of nitric acid, initial distribution ratios remained constant over the whole examined dose range up to 300 kGy. For qualitative determination of radiolysis products, HPLC-MS measurements were performed. The protective effect of nitric acid was confirmed, since in samples irradiated with acid contact, no degradation products were observed, but only addition products of the 1-octanol molecule to the CyMe4BTBP molecule

Revisiting James March (1991): Whither Exploration and Exploitation

We revisit March’s seminal 1991 article, “Exploration and exploitation in organizational learning”, and analyze the impact it has had on scholarly thinking, providing a comprehensive and structured review of the extensive and diverse research inspired by this publication. We show that although this influence has changed significantly over the years, there are still unexplored opportunities left by this seminal work. Our approach enables us to identify promising directions for future research that reinforce the themes anchored in March’s article. In particular, we call for reconnecting current research to the behavioral roots of this article and uncovering the microfoundations of exploration and exploitation. Our analysis further identifies opportunities for integrating this framework with resource-based theories and considering how exploration and exploitation can be sourced and integrated within and across organizational boundaries. Finally, our analysis reveals prospects for extending the notions of exploration and exploitation to new domains, but we caution that such domains should be clearly delineated. We conclude with a call for further research on the antecedents of exploration and exploitation and for studying their underexplored dimensions

Comprehension as social and intellectual practice: Rebuilding curriculum in low socioeconomic and cultural minority schools

This article reframes the concept of comprehension as a social and intellectual practice. It reviews current approaches to reading instruction for linguistically and culturally diverse and low socioeconomic students, noting an emphasis on comprehension as autonomous skills. The Four Resources model (Freebody & Luke, 1990) is used to make the case for the integration of comprehension instruction with an emphasis on student cultural and community knowledge, and substantive intellectual and sociocultural content in elementary school curricula. Illustrations are drawn from research underway on the teaching of literacy in primary schools in low SES communities

Gamma and pulsed electron radiolysis studies of CyMe4BTBP and CyMe4BTPhen: Identification of radiolysis products and effects on the hydrometallurgical separation of trivalent actinides and lanthanides

The radiolytic stability of the highly selective ligands CyMe4BTBP and CyMe4BTPhen against ionizing gamma radiation was studied in 1-octanol solution. CyMe4BTBP and CyMe4BTPhen are important extractants for a potential treatment of used nuclear fuel. They were studied under identical experimental conditions to directly compare the effects of gamma and pulsed electron radiolysis on the ligands and systematically study the influence of structural changes in the ligand backbone. Distribution ratios of Am3+, Cm3+ and Eu3+, the residual concentration of CyMe4BTBP and CyMe4BTPhen in solution, and the formation of radiolysis products were studied as a function of absorbed gamma dose and presence of an acidic aqueous phase during irradiation. Quantitative and semi-quantitative analyses were used to elucidate the radiolysis mechanism for both ligands. Addition products of alpha-hydroxyoctyl radicals formed through radiolysis of the 1-octanol diluent to the ligand molecules were identified as the predominant radiolysis products. These addition products also extract trivalent metal ions, as distribution ratios remained high although the parent molecule concentrations decreased. Therefore, the utilization time of a solvent using these extractants under the harsh conditions of used nuclear fuel treatment could be considerably longer than expected. Understanding the radiolysis mechanism is crucial for designing more radiation resistant extractants

An overview of solvent extraction processes developed in Europe for advanced nuclear fuel recycling, Part 2 — homogeneous recycling

The hydrometallurgical separation concepts for the recycling of irradiated nuclear fuels developed in Europe are presented and discussed. Whilst Part 1 of the review focused on concepts for heterogeneous recycling of minor actinides, this article focuses on group recycling of transuranic actinides, which would support homogeneous recycling scenarios. Most of these concepts were developed within European collaborative projects and involve solvent extraction processes separating all the actinides (U-Cm) in two cycles. The first cycle uses a monoamide extractant to recover uranium leaving all the transuranic actinides in the aqueous raffinate with the fission products. The second cycle aims for a group recovery of the transuranium elements and several strategies have been proposed for this stage. In this review article, the various solvent extraction processes are summarised and the key features of the process schemes are compared

Processing of Thionin Precursors in Barley Leaves by a Vacuolar Proteinase

Thionins are synthesized as precursors with a signal peptide and a long C-terminal acidic peptide that is post-translationally processed. A fusion protein including the maltose-binding protein from Eschrrichia coli (MalE), thionin DG3 froin barley leaves, and its acidic C-terminal peptide has been used to obtain antibodies that recognize both domains of the precursor. In barley leaf sections. mature thionins accuinulated in the vacuolar content, while the acidic peptide was not detected in any cell fraction. Brefeldin A and inonensin inhibited processing of the precursor but its export from the microsomal fraction was not inhibited. Both purified vacuoles aiid an acid (pH 5.5) extract from leaves processed the fusion protein into a MalE-thionin and an acidic peptide fragment. A 70-kDa proteinase that effected this cleavage was purified froin the acid extract. Processing of the fusion protein by both lysed vacuoles and the purified proteinase was inhibited by Zn2+ and by Cu2+, but not by inhibitors of the previously described vacuolar processing thiol or aspartic proteinases. In vivo processing of the thionin precursor in leaf sections was also inhibited by Zn+, and Cu2+, Variants of the fusion protein with altered processing sites that represented thme of thionin precursors from different taxa were readily processed by the proteinase, whereas changing the polarity of either the C-terminal or N-terminal residues of the processing site prevented cleavage by the proteinase

Highly efficient separation of actinides from lanthanides by a phenanthroline-derived bis-triazine ligand

The synthesis, lanthanide complexation, and solvent ex- traction of actinide(III) and lanthanide(III) radiotracers from nitric acid solutions by a phenanthroline-derived quadridentate bis-triazine ligand are described. The ligand separates Am(III) and Cm(III) from the lanthanides with remarkably high efficiency, high selectivity, and fast extraction kinetics compared to its 2,2'-bipyridine counterpart. Structures of the 1:2 bis-complexes of the ligand with Eu(III) and Yb(III) were elucidated by X-ray crystallography and force field calculations, respec-tively. The Eu(III) bis-complex is the first 1:2 bis-complex of a quadridentate bis-triazine ligand to be characterized by crystallography. The faster rates of extraction were verified by kinetics measurements using the rotating membrane cell technique in several diluents. The improved kinetics of metal ion extraction are related to the higher surface activity of the ligand at the phase interface. The improvement in the ligand's properties on replacing the bipyridine unit with a phenanthroline unit far exceeds what was anticipated based on ligand design alone