In situ measurements of subsurface contaminants with a multi-channel laser-induced fluorescence system.

A new multi-channel laser-induced fluorescence (LIF) probe with novel optical fiber probe geometry has been designed and integrated into a cone penetrometer testing (CPT) system for in situ contamination detection. The system is capable of collecting excitation and emission matrices (EEMs) of subsurface contaminants as a function of depth in seconds. Compared to our previous multi-channel LIF-CPT system, the new system is faster and more compact, with reduced probe size and sampling area. This article describes the first field demonstration of the system at Hanscom Air Force Base, Massachusetts. One contaminated site within the base was characterized through in situ measurements of 26 LIF-CPT pushes. To validate the LIF results, core samples taken at five locations were analyzed by both on-site LIF measurements and by off-site laboratory analyses with EPA methods. The comparison of the LIF and laboratory results is presented, along with the results of the in situ measurements.     

Influence of bridging atom on the vertical phase separation of low band gap bulk heterojunction solar cells

Vertical phase separation of the polymer and fullerene molecules in bulk heterojunction organic solar cells influences the exciton dissociation, charge carrier transport and collection. This work compares the vertical phase separation of poly[2,1,3‐benzothiadiazole‐4,7‐diyl[4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta [2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl]] (C‐PCPDTBT):[6,6]‐phenyl C71 butyric acid methyl ester (PC₇₁BM) and poly[2,1,3‐benzothiadiazole‐4,7‐diyl[4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta [2,1‐b:3,4‐b′]dithiophene‐siloe2,6‐diyl]] (Si‐PCPDTBT):PC₇₁BM blend films, using X‐ray photoemission spectroscopy depth profiles. The difference between the two polymers is the bridging atom, which is carbon for C‐PCPDTBT and silicon for Si‐PCPDTBT. Si‐PCPDTBT exhibits enhanced polymer chain packing and crystallinity. We believe this enhanced chain packing provides a driving force during film drying which alters the vertical morphology. The different nature of vertical phase separation plays a role in determining the increased device performance observed for Si‐PCPDTBT:PC₇₁BM solar cells. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Kernel based quadrature on spheres and other homogeneous spaces

Quadrature formulas for spheres, the rotation group, and other compact, homogeneous manifolds are important in a number of applications and have been the subject of recent research. The main purpose of this paper is to study coordinate independent quadrature (or cubature) formulas associated with certain classes of positive definite and conditionally positive definite kernels that are invariant under the group action of the homogeneous manifold. In particular, we show that these formulas are accurate—optimally so in many cases—and stable under an increasing number of nodes and in the presence of noise, provided the set $X$ of quadrature nodes is quasi-uniform. The stability results are new in all cases. In addition, we may use these quadrature formulas to obtain similar formulas for manifolds diffeomorphic to $\mathbb S ^n$ , oblate spheroids for instance. The weights are obtained by solving a single linear system. For $\mathbb S ^2$ , and the restricted thin plate spline kernel $r^2\log r$ , these weights can be computed for two-thirds of a million nodes, using a preconditioned iterative technique introduced by us.     

Singularities of the solution of a mixed problem for a general second order elliptic equation and boundary stabilizationof the wave equation

We deal here with a second order elliptic mixed problem which is posed in a regular open bounded domain of . We study the regularity of its solution. We apply our results to the boundary stabilization of the wave equation.     

Analytical methods for monitoring contaminants in food—An industrial perspective

Incoming legislation on the registration, evaluation, authorisation and restriction of chemical substances places responsibility on the chemical industry, including downstream users of chemicals, to provide appropriate safety information with which to improve the protection of human health and the environment through the better and earlier identification of the intrinsic properties of chemical substances. Food consumption is only one of several potential exposure routes, but if industrial chemicals enter the food chain, the diet may be a significant pathway of human exposure. Consequently strong measures are taken to protect the integrity of the human food chain and these are constantly revised to address perceived chemical safety threats. In order to understand the risk presented by the possible presence of a chemical residue in food, knowledge is required of its toxicology and of the level of exposure. Reliable exposure assessment requires robust analytical methodology. Existing standards for the validation and performance evaluation of methods have led to improved analytical capability and better inter-laboratory agreement of results. However, increasing the availability of robust, cost-effective methodology should be the benchmark for future developments in the field of food chemical residue analysis. Chromatography meets the needs of target analyses well and largely provides the selectivity of measurement needed to assess compliance with food regulatory limits. However, to keep pace with the increased need for expanded analytical capability – faster throughput, more analytes per sample – chromatographic separation capability still needs to grow. In this respect, orthogonal separation techniques and multi-dimensional chromatography are key tools for the future.     

Further studies on vinamidinium salt amine exchange reactions, borohydride reductions and subsequent transformations

Studies directed at the amine exchange reaction of vinamidinium salts followed by sodium borohydride reduction to secondary and tertiary allylic amines are described. The tertiary allylic amines were alkylated and subjected to base mediated rearrangement to yield a variety of highly functionalized tertiary homoallylic amines.     

A simple approach to coordination compounds of the pentacyanocyclopentadienide anion

Deprotonation of [Et(3)NH][C(5)(CN)(5)] with metal bases provides a very simple approach to coordination compounds containing the pentacyanocyclopentadienide anion [C(5)(CN)(5)](-) (1). The three-dimensional polymer [Na(thf)(1.5)(1)](∞) and the molecular dimer [{(tmeda)(2)Na(1)}(2)] are obtained by reaction of this precursor with NaH in the presence of thf or tmeda (Me(2)NCH(2)CH(2)NMe(2)). Their single-crystal X-ray structures both reveal σ-bonded C≡N-Na arrangements and π stacking between [C(5)(CN)(5)](-) ions. DFT calculations on the [C(5)(CN)(5)](-) ion have been used to investigate the structures and bonding in [Na(thf)(1.5)(1)](∞) and [{(tmeda)(2)Na(1)}(2)]. The absence of π bonding of the metal ions in both complexes is due to dispersion of the negative charge from the C(5) ring unit to the C[triple chemical bond]N groups in the [C(5)(CN)(5)](-) ion, making the coordination chemistry of this anion distinctly different from that of cyclopentadienide C(5)H(5)(-).     

Development of a Controlled Release System for Risperidone Using Polypyrrole: Mechanistic Studies

Polypyrrole (PPY) film has been selected as a platform material for drug delivery due to its inherent conductivity, ease of preparation and apparent biocompatibility. PPY films were prepared containing the antipsychotic drug risperidone as a model compound. Drug release profiles could be altered by applying different electrical stimulation to these films. Atomic force microscopy was used to investigate changes in PPY film thickness when different stimuli were applied. The highest levels of drug release were observed when PPY was reduced; this was accompanied by expansion of the film. Technology such as this could be utilized for implantable drug delivery devices, where the dose could be adjusted by external signaling.     

Flexibility and swing effect on the adsorption of energy-related gases on ZIF-8: combined experimental and simulation study

ZIF-8, a prototypical zeolitic porous coordination polymer, prepared via the self-assembly of tetrahedral atoms (e.g. Zn and Co) and organic imidazolate linkers, presents large cavities which are interconnected by narrow windows that allow, in principle, molecular sieving. However, ZIF-8 shows flexibility due to the swing of the imidazolate linkers, which results in the adsorption of molecules which are too large to fit through the narrow window. In this work, we assess the impact of this flexibility, previously only observed for nitrogen, and the level of agreement between the experimental and simulated isotherms of different energy-related gases on ZIF-8 (CO(2), CH(4) and alkanes). We combine experimental gas adsorption with GCMC simulations, using generic and adjusted force fields and DFT calculations with the Grimme dispersion correction. By solely adapting the UFF force field to reduce the Lennard-Jones parameter ε, we achieve excellent agreement between the simulated and experimental results not only for ZIF-8 but also for ZIF-20, where the transferability of the adapted force field is successfully tested. Regarding ZIF-8, we show that two different structural configurations are needed to properly describe the adsorption performance of this material, demonstrating that ZIF-8 is undergoing a structural change during gas adsorption. DFT calculations with the Grimme dispersion correction are consistent with the GCMC and experimental observations, illustrating the thermodynamics of the CH(4) adsorption sites and confirming the existence of a new adsorption site with a high binding energy within the 4-ring window of ZIF-8.