XANES speciation of mercury in three mining districts – Almadén,Asturias (Spain), Idria (Slovenia)

The mobility, bioavailability and toxicity of mercury in the environment strongly depend on the chemical species in which it is present in soil, sediments, water or air. In mining districts, differences in mobility and bioavailability of mercury mainly arise from the different type of mineralization and ore processing. In this work, synchrotron‐based X‐ray absorption near‐edge spectroscopy (XANES) has been taken advantage of to study the speciation of mercury in geological samples from three of the largest European mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). XANES has been complemented with a single extraction protocol for the determination of Hg mobility. Ore, calcines, dump material, soil, sediment and suspended particles from the three sites have been considered in the study. In the three sites, rather insoluble sulfide compounds (cinnabar and metacinnabar) were found to predominate. Minor amounts of more soluble mercury compounds (chlorides and sulfates) were also identified in some samples. Single extraction procedures have put forward a strong dependence of the mobility with the concentration of chlorides and sulfates. Differences in efficiency of roasting furnaces from the three sites have been found.     

Editable machine learning models? A rule-based framework for user studies of explainability

Advances in Data Analysis and Classification - So far, most user studies dealing with comprehensibility of machine learning models have used questionnaires or surveys to acquire input from...     

On nonlocal symmetries for the Krichever–Novikov equation

We construct new infinite hierarchies of nonlocal symmetries and cosymmetries for the Krichever–Novikov equation using the inverse of the fourth-order recursion operator of the latter.     

Nonlocal Symmetries of Integrable Linearly Degenerate Equations: A Comparative Study

We continue the study of Lax integrable equations. We consider four three-dimensional equations: (1) the rdDym equation u_ty = u_xu_xy ? u_yu_xx, (2) the Pavlov equation u_yy = u_tx + u_yu_xx ? u_xu_xy, (3) the universal hierarchy equation u_yy = u_tu_xy ? u_yu_tx, and (4) the modified Veronese web equation u_ty = u_tu_xy ? u_yu_tx. For each equation, expanding the known Lax pairs in formal series in the spectral parameter, we construct two differential coverings and completely describe the nonlocal symmetry algebras associated with these coverings. For all four pairs of coverings, the obtained Lie algebras of symmetries manifest similar (but not identical) structures; they are (semi)direct sums of the Witt algebra, the algebra of vector fields on the line, and loop algebras, all of which contain a component of finite grading. We also discuss actions of recursion operators on shadows of nonlocal symmetries.     

Intercalation of a Heterocyclic Ligand between Quartets in a G-Rich Tetrahelical Structure

YES G-rich oligonucleotide VK2 folds into an AGCGA-quadruplex tetrahelical structure distinct and significantly different from G-quadruplexes, even though it contains four G₃ tracts. Herein, a bis-quinolinium ligand 360A with high affinity for G-quadruplex structures and selective telomerase inhibition is shown to strongly bind to VK2. Upon binding, 360A does not induce a conformational switch from VK2 to an expected G-quadruplex. In contrast, NMR structural study revealed formation of a well-defined VK2–360A complex with a 1:1 binding stoichiometry, in which 360A intercalates between GAGA- and GCGC-quartets in the central cavity of VK2. This is the first high-resolution structure of a G-quadruplex ligand intercalating into a G-rich tetrahelical fold. This unique mode of ligand binding into tetrahelical DNA architecture offers insights into the stabilization of an AGCGA-quadruplex by a heterocyclic ligand and provides guidelines for rational design of novel VK2 binding molecules with selectivity for different DNA secondary structures.     

Characterization of Mercury Contamination Surrounding a Chloralkali Production Facility in Tuzla,Bosnia and Herzegovina

Tuzla is among the most polluted cities of Bosnia and Herzegovina. The main source of pollution in the area is soil heavily contaminated by mercury released from a former chloralkali plant. This paper is focused on the characterization of mercury contaminated soil and air surrounding the chloralkali plant. In soil, the mobility and transformation of mercury were investigated by sequential extraction, while the methylation and reduction potentials were determined by the use of a radioactive tracer. Mercury emission from soil was determined by laboratory and by flux chamber measurements in the field. In addition, mercury concentrations in air were estimated by the analysis of air and the transplanted lichen Hypogymnia physodes. Mercury in soils in the vicinity of the chloralkali plant exceeded the background value by a factor of more than 3000. The fractionation of mercury in surface soil by sequential extraction showed that the mercury in soil was primarily bound to organic matter and a fraction containing elemental mercury and mercury (I) chloride is also significant. The obtained methylation and reduction potentials are low. The mercury flux from soil was estimated by two approaches. Fluxes of up to 8000?ng/m²/day were measured at the most polluted site; evaporation from soil was shown to be the primary source of elevated mercury in air. Air concentration mapping also revealed other sources of mercury; the most likely is the 715 MW coal power plant in the vicinity of former chloralkali facility.     

Computational experience with Davidon's least-square algorithm

Computational results are presented for Davidon's new least-square algorithm. Computational experience with this algorithm is reported which motivated the development of a production code version of the algorithm. Several heuristic modifications, which have been added, are described. Fifteen zero-residual test problems have been used in comparing the new production code version with two established versions of the Levenberg-Marquardt algorithm. The production code version of Davidon's least-square algorithm performed faster and used less function evaluations than the Levenberg-Marquardt algorithm in almost every case of the test problems.It is a pleasure to acknowledge and thank M. Thomas, R. & I. Consultant, Western Illinois University Computer Center, for writing the timing routine and taking the time to run the comparison tests on the IBM 360/50. Part of this work was also performed at the Applied Mathematics Division of Argonne National Laboratory under the auspices of the US Energy Research and Development Administration.     

Coverings over lax integrable equations and their nonlocal symmetries

We consider the three-dimensional rdDym equation u_ty = u_xu_xy ?u_yu_xx. Using the known Lax representation with a nonremovable parameter and two hierarchies of nonlocal conservation laws associated with it, we describe the algebras of nonlocal symmetries in the corresponding coverings.