Complexing capacity of low-level radioactive waste leachates for Co and Cd using an ion-exchange technique

Low-level radioactive wastes (LLRW) intended for disposal at Chalk River laboratories (CRL) are composed primarily (>90% by volume) of organic material (paper, used clothing, packaging material, mop heads, etc.). Upon contact with water, microbial degradation of this material will produce dissolved organic matter (DOM) which has the potential to change the speciation and mobility of radionuclides in soils. The determination of the aqueous speciation of nuclides will provide a tool that will enable a better prediction of the behaviour of nuclides and their potential to migrate in soils.

This work is one aspect of the characterisation of the DOM produced by the microbial degradation of LLRW. An ion-exchange technique was set up to demonstrate the applicability of the method to determine the complexing capacity of the DOM in a difficult matrix. Leachates from a LLRW degradation experiment were used with two radioisotopes (¹⁰⁹Cd and ⁶⁰Co). The method allows the determination of the free-ion content of a metal in a solution, which also leads to the determination of the complexed fraction.

The leachate matrix consisted of 0.1 M ionic strength of inorganic salts, with 4177 mg C/l of DOM. The complexing capacity of the DOM in the leachates was 50 μg/l for Co, and 0.54 μg/l for Cd. This represents 0.0028% and 0.000015% of the available DOM sites to Co and Cd, respectively. The conditional stability constant of the DOM with Cd was slightly higher (log β = 1.98) than that of acetic acid, whereas it was ambiguous for Co (log β = 2.02 or 2.54). DOM fouling did not constitute a problem, and the method could be used for other radionuclides and metals.     

Recognizing a something when your library sees it

Advances are needed in random-display technologies to more tightly link drug actions and functions to the genes that control physiological processes. The reports discussed here explore two sides of these issues-generating new library formats and identifying the targets of drug ligands.     

Minimization of some non-differentiable functionals by the Augmented Lagrangian Method of Hestenes and Powell

The Augmented Lagrangian Method of Hestenes and Powell is presented here in a more general case, including Fenchel's duality, using some recent results of R. T. Rockafellar which are here extended. It is shown that for some functionals which contain a non-differentiable term which is the support function of a convex set, the Augmented Lagrangian Method provides a natural way to marry standard duality techniques and regularisation techniques. An application to visco-plastic flows is presented and numerical results are given. A convergence proof is given for the algorithm used. Another application to elasto-plastic torsion is also signaled.     

Preparation and characterization of oxorhenium(V) complexes with 2,2'-biimidazole: the strong affinity of coordinated biimidazole for chloride ions via N-H...Cl- hydrogen bonding

N,N'-Dimethylbiimidazole and bipyridine (N-N) react with ReOCl3(OPPh3)(Me2S) to give mer-ReOCl3(N-N) compounds. Nonmethylated biimidazole forms a trans-O,O [ReOCl2(OPPh3)(biimH2)]+ cation, which is tightly associated with the Cl- counterion via N-H...Cl- hydrogen bonding. Hydrolysis of ReOCl3(biimMe2) in wet acetone (5% water) leads to the linear oxo-bridged dinuclear species [(OReCl2(biimMe2)2(mu-O)] containing chelated biimMe2. Acetone solutions containing only 1% water yield the bent oxo-bridged dinuclear species [(OReCl2)2(mu-O)(mu-biimMe2)2], where each Re center retains the ReO2Cl2N2 coordination but the biimMe2 ligands are bridging. The linear oxo-bridged [(OReCl2(biimH2)2(mu-O)] complex obtained with nonmethylated biimidazole includes two Cl- ions held via N-H...Cl- hydrogen bonds, leading to a dianionic [(OReCl2(biimH2...Cl)2(mu-O)]2- unit in the crystals of the PPh4+ salt. The compounds are characterized by IR and NMR spectroscopies, and the structures of [ReOCl2(OPPh3)(biimH2)]Cl, [(OReCl2(biimH2)2(mu-O)](PPh4Cl)(2).2H2O, and [(OReCl2)2(mu-O)(mu-biimMe2)2].acetone are determined by X-ray diffraction.     

VO2 thin films based active and passive thermochromic devices for energy management applications

VO₂ thin films were fabricated by argon ion beam assisted non-reactive ac dual magnetron sputtering followed by carefully controlled thermal oxidation. This method is known to give high quality compact thin films with uniform high deposition rates. Thin films deposited on both bare glass and indium tin-oxide (ITO) coated glass substrates were studied, respectively, as passive and active thermochromic devices for their electrical and optical switching behaviors. Thin films varying in thicknesses from 65 to 250 nm were investigated. ITO film was used as an integrated heating device to activate the phase transition via an applied bias voltage. Such structures were found to bear several advantages from an application point of view.     

Classical Limit and Quantum Logic

The analysis of the classical limit of quantum mechanics usually focuses on the state of the system. The general idea is to explain the disappearance of the interference terms of quantum states appealing to the decoherence process induced by the environment. However, in these approaches it is not explained how the structure of quantum properties becomes classical. In this paper, we consider the classical limit from a different perspective. We consider the set of properties of a quantum system and we study the quantum-to-classical transition of its logical structure. The aim is to open the door to a new study based on dynamical logics, that is, logics that change over time. In particular, we appeal to the notion of hybrid logics to describe semiclassical systems. Moreover, we consider systems with many characteristic decoherence times, whose sublattices of properties become distributive at different times.     

Photovoltaic effect and optical absorption in MoS2

An investigation of the Schottky barriers of a number of metals on natural P-type MoS₂ was undertaken. The spectral dependence of the photovoltaic effect of all the metal barriers show two distinct features at 1.38 and 1.68 eV below the direct bandgap at 1.8 eV. A low energy edge at 1.2 eV is invariably observed for metal barriers on MoS₂. Absorption measurements performed over the same energy range indicate that the features observed in the photoresponse spectra are related to indirect transitions in MoS₂, in agreement with recent band calculations. Preliminary data indicate that MoS₂ based Schottky barrier solar cells may be of interest.