Anomalous fluoride concentration in groundwater—is it natural or pollution? A stable isotope approach

Fluoride anomalies (up to 11 mg/l) have been detected in groundwater of the central region of Rio Grande do Sul State, Southern Brazil, in an area where fluorosis is endemic. Two hypotheses are investigated concerning the fluoride origin: lithochemical affiliation from regional rock or contamination by fertilisers application. These hypotheses are discussed based on the stable isotope data of water, nitrate, and sulphate, which indicates that the local precipitation is the main groundwater recharge source. The isotopic composition of groundwater sulphate is similar to that of fertiliser sulphate. However, a conclusive assignment of groundwater sulphate to fertiliser origin is not indicated because further possible sulphate sources fall into the same isotopic range. In contrast, the isotopic composition of dissolved nitrate suggests that there is no direct relationship to the use of NPK fertilisers. Hence, an origin of the high fluoride content in groundwater related to long-term rock–water interactions seems likely.     

The effect of closed-loop feedback control on scalar mixing in a plane shear layer

The effect of feedback on mixing in a plane shear layer was studied using temperature as an analog to species concentration. Mixing was quantified using temperature measurements made by an array of cold-wire sensors. Upstream of the cold-wire sensors, a schlieren imager measured the cross-stream position of the temperature interface between the two streams before the primary vortical structures had formed. Surface heaters mounted on the flow partition were used as control actuators. Feeding the gained output from the interface position sensor back to the surface heaters closed the loop and created resonance and out-of-resonance conditions in the flow, both of which increased mixing. The feedback gains were adaptively modified in real time to maximize mixing at a given streamwise station. Finally, it was found that deliberately introducing streamwise vorticity, and then choosing feedback gains that strengthen these streamwise vortices, can greatly enhance mixing.     

On the cosmic-ray spectra of three-body lepton-flavor-violating dark matter decays

We consider possible leptonic three-body decays of spin-1/2, charge-asymmetric dark matter. Assuming a general Dirac structure for the four-fermion contact interactions of interest, we study the cosmic-ray electron and positron spectra and show that good fits to the current data can be obtained for both charged-lepton-flavor-conserving and flavor-violating decay channels. We find that different choices for the Dirac structure of the underlying decay operator can be significantly compensated by different choices for the dark matter mass and lifetime. The decay modes we consider provide differing predictions for the cosmic-ray positron fraction at energies higher than those currently probed at the PAMELA experiment; these predictions might be tested at cosmic-ray detectors like AMS-02.     

Studying electronic transport in polyazulene-ionic liquid systems using infrared vibrational spectroscopy

This paper presents an in situ spectroelectrochemical characterization of polyazulene (PAz) and PAz-C(60) composite films using Fourier Transform Infrared Attenuated Total Reflection (FTIR-ATR) spectroscopy. In situ FTIR-ATR spectra were recorded simultaneously as the films were charged and discharged electrochemically. The aim was to clarify how the use of ILs and the addition of C(60) affected the electronic transport and structural changes occurring in PAz during electrochemical charging. We found that electrosynthesis of PAz in an IL lowered the oxidation potential of the film and improved its electroactivity. The FTIR-ATR data also suggest that PAz with a longer effective conjugation length is obtained during electrosynthesis when using ILs. With in situ FTIR-ATR it is possible to quite accurately determine the onset potential for oxidation/reduction. These values are important since they determine the suitability of the polymer for a specific application. Our experiments indicate that two types of charge carriers are formed during electrochemical oxidation of PAz in an IL. Furthermore, their formation is strongly affected by the addition of C(60) into the film. The type of charge carrier formed affects the electronic and possibly also ionic transport within the film. The inclusion of C(60) into PAz influenced the optical and structural properties considerably. In situ FTIR-ATR is also an extremely useful method for studying the potential stability of an IL during electrochemical cycling. We showed that cathodic decomposition of N,N-butyl-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][Tf(2)N]) occurs at less negative potentials than those determined electrochemically.     

Imidotungsten(VI) complexes with chelating amino and imino phenolates

The reaction of WOCl(4) with 2,4-di-tert-butyl-6-((isopropylamino)methyl)phenol followed by the reaction with phenyl isocyanate leads to the formation of imidotungsten(VI) complex [W(NPh)Cl(3)(OC(6)H(3)(CH(2)NH-i-Pr)-2-t-Bu(2)-4,6)] 4 with a chelating aminophenolate ligand. When the same procedure was applied using aminophenols with bulkier substituents in the amino group, the final product was an unexpected Schiff-base complex [W(NPh)Cl(3)(OC(6)H(3)(CH=NPh)-2-t-Bu(2)-4,6)] 5, where the ligand is derived from 2,4-di-tert-butyl-6-((phenylimino)methyl)phenol. Complex 5 is also formed in the thermal degradation of 4. On the whole, 5 appears to be formed by a disproportionation of intermediate compounds, which are analogous to complex 4. The solid-state structures of 4 and 5 have been determined by X-ray crystallography whereas the solution structures were studied by (1)H and (13)C NMR.     

Disposable roll-to-roll hot embossed electrophoresis chip for detection of antibiotic resistance gene mecA in bacteria

We present a high-throughput roll-to-roll (R2R) manufacturing process for foil-based polymethyl methacrylate (PMMA) chips of excellent optical quality. These disposable, R2R hot embossed microfluidic chips are used for the identification of the antibiotic resistance gene mecA in Staphylococcus epidermidis. R2R hot embossing is an emerging manufacturing technology for polymer microfluidic devices. It is based on continuous feeding of a thermoplastic foil through a pressurized area between a heated embossing cylinder and a blank counter cylinder. Although mass fabrication of foil-based microfluidic chips and their use for biological applications were foreseen already some years ago, no such studies have been published previously.     

Nanocomposites Prepared by Solution Blending: Microstructure and Mechanical Properties

Composites of poly(vinyl chloride) (PVC) filled with micron‐ and nanosized calcium carbonate (CaCO₃) particles were prepared by solution blending. The influences of particle size and CaCO₃ content on the microstructure and mechanical properties of the PVC composites were investigated by means of polarized optical microscopy and mechanical testing. The polarized optical microscope images revealed that nanosized CaCO₃ particles were more agglomerated than micron‐sized CaCO₃ particles and the amount of agglomerates increased with increasing particle content. PVC/CaCO₃‐0.22 composites (PVC nanocomposite filled with 220‐nm‐particle‐sized CaCO₃) 5 phr CaCO₃ content had the maximum tensile strength. The Young's modulus of all composites increased with increasing particle content. The energy at break of all composites showed a decreasing trend as a function of CaCO₃ content and varied with particle size.     

Geometric Variational Crimes: Hilbert Complexes,Finite Element Exterior Calculus,and Problems on Hypersurfaces

A recent paper of Arnold, Falk, and Winther (Bull. Am. Math. Soc. 47:281–354, 2010) showed that a large class of mixed finite element methods can be formulated naturally on Hilbert complexes, where using a Galerkin-like approach, one solves a variational problem on a finite-dimensional subcomplex. In a seemingly unrelated research direction, Dziuk (Lecture Notes in Math., vol. 1357, pp. 142–155, 1988) analyzed a class of nodal finite elements for the Laplace–Beltrami equation on smooth 2-surfaces approximated by a piecewise-linear triangulation; Demlow later extended this analysis (SIAM J. Numer. Anal. 47:805–827, 2009) to 3-surfaces, as well as to higher-order surface approximation. In this article, we bring these lines of research together, first developing a framework for the analysis of variational crimes in abstract Hilbert complexes, and then applying this abstract framework to the setting of finite element exterior calculus on hypersurfaces. Our framework extends the work of Arnold, Falk, and Winther to problems that violate their subcomplex assumption, allowing for the extension of finite element exterior calculus to approximate domains, most notably the Hodge–de Rham complex on approximate manifolds. As an application of the latter, we recover Dziuk’s and Demlow’s a priori estimates for 2- and 3-surfaces, demonstrating that surface finite element methods can be analyzed completely within this abstract framework. Moreover, our results generalize these earlier estimates dramatically, extending them from nodal finite elements for Laplace–Beltrami to mixed finite elements for the Hodge Laplacian, and from 2- and 3-dimensional hypersurfaces to those of arbitrary dimension. By developing this analytical framework using a combination of general tools from differential geometry and functional analysis, we are led to a more geometric analysis of surface finite element methods, whereby the main results become more transparent.     

Addressing the Clumsiness Loophole in a Leggett-Garg Test of Macrorealism

The rise of quantum information theory has lent new relevance to experimental tests for non-classicality, particularly in controversial cases such as adiabatic quantum computing superconducting circuits. The Leggett-Garg inequality is a “Bell inequality in time” designed to indicate whether a single quantum system behaves in a macrorealistic fashion. Unfortunately, a violation of the inequality can only show that the system is either (i) non-macrorealistic or (ii) macrorealistic but subjected to a measurement technique that happens to disturb the system. The “clumsiness” loophole (ii) provides reliable refuge for the stubborn macrorealist, who can invoke it to brand recent experimental and theoretical work on the Leggett-Garg test inconclusive. Here, we present a revised Leggett-Garg protocol that permits one to conclude that a system is either (i) non-macrorealistic or (ii) macrorealistic but with the property that two seemingly non-invasive measurements can somehow collude and strongly disturb the system. By providing an explicit check of the invasiveness of the measurements, the protocol replaces the clumsiness loophole with a significantly smaller “collusion” loophole.     

Coherent-mode representation of supercontinuum

We apply the coherent-mode expansion to correlation functions used to describe the coherence properties of supercontinuum generated in nonlinear ?bers. We show that the leading term of the expansion represents the quasi-coherent part of the ?eld while the quasi-stationary part is embedded into the higher-order modes. The evolution of the modal expansion and the number of modes needed to describe the supercontinuum ?eld are also discussed.