Time-integrated monitoring of polycyclic aromatic hydrocarbons (Pahs) in groundwater using the ceramic dosimeter passive sampling device

Passive sampling relies on the uptake of contaminants into appropriate sampling devices along a diffusion gradient without using pumps or bailers. Thus, for example, in groundwater sampling, changes to flow due to pumping can be avoided. If the diffusion gradient can be maintained for extended periods, contaminants can be sampled continuously over time without any action, allowing to determine time-weighted average contaminant concentrations. We here show that the Ceramic Dosimeter, a solid receiving phase passive sampler using a ceramic membrane as sorbent container and diffusion barrier, can be used without calibration for the long-term monitoring of polycyclic aromatic hydrocarbons (PAHs) in groundwater.     

Synthesis of the anti and syn isomers of thieno[f,f ']bis[1]benzothiophene. Comparison of the optical and electrochemical properties of the anti and syn isomers

We report isomer-pure synthesis of thieno[2,3-f:5,4-f ']bis[1]benzothiophene and thieno[3,2-f:4,5-f ']bis[1]benzothiophene, the anti and syn isomers of a pentacyclic compound consisting of alternating thiophene and benzene rings. The optical and electrochemical properties of both are reported. In the anti isomer, the ribbonlike embedding of three thiophene units leads to a near-planar molecule with favorable pi-pi stacking behavior in the solid state as shown by X-ray crystal structure analysis.     

Evaluating the Potential for Smoke from Stubble Burning to Taint Grapes and Wine

It has been well established that bushfire/wildfire smoke can taint grapes (and therefore wine), depending on the timing and duration of exposure, but the risk of smoke contamination from stubble burning (a practice employed by some grain growers to prepare farmland for sowing) has not yet been established. This study exposed excised bunches of grapes to smoke from combustion of barley straw and pea stubble windrows to investigate the potential for stubble burning to elicit smoke taint. Increased levels of volatile phenols (i.e., chemical markers of smoke taint) were detected in grapes exposed to barley straw smoke (relative to control grapes), with smoke density and the duration of smoke exposure influencing grape volatile phenols. However, the sensory panel did not perceive wine made from grapes exposed to low-density smoke to be tainted, despite the presence of low levels of syringol providing compositional evidence of smoke exposure. During the pea stubble burn, grapes positioned amongst the burning windrows or on the edge of the pea paddock were exposed to smoke for ~15–20 and 30–45 min, respectively, but this only resulted in 1 µg/kg differences in the cresol and/or syringol concentrations of smoke-affected grapes (and 1 µg/L differences for wine), relative to controls. A small, but significant increase in the intensity of smoke aroma and burnt rubber flavor of wine made from the grapes positioned amongst the burning pea stubble windrows provided the only sensory evidence of any smoke taint. As such, had vineyards been located immediately downwind from the pea stubble burn, it is unlikely that there would have been any smoke contamination of unharvested grapes.     

Multicategory Classification by Support Vector Machines

We examine the problem of how to discriminate between objects of three or more classes. Specifically, we investigate how two-class discrimination methods can be extended to the multiclass case. We show how the linear programming (LP) approaches based on the work of Mangasarian and quadratic programming (QP) approaches based on Vapnik's Support Vector Machine (SVM) can be combined to yield two new approaches to the multiclass problem. In LP multiclass discrimination, a single linear program is used to construct a piecewise-linear classification function. In our proposed multiclass SVM method, a single quadratic program is used to construct a piecewise-nonlinear classification function. Each piece of this function can take the form of a polynomial, a radial basis function, or even a neural network. For the k > 2-class problems, the SVM method as originally proposed required the construction of a two-class SVM to separate each class from the remaining classes. Similarily, k two-class linear programs can be used for the multiclass problem. We performed an empirical study of the original LP method, the proposed k LP method, the proposed single QP method and the original k QP methods. We discuss the advantages and disadvantages of each approach.     

Magnitudes and orientations of the 15N chemical shift tensor of [1-15N]-2'-deoxyguanosine determined on a polycrystalline sample by two-dimensional solid-state NMR spectroscopy.

The magnitudes and orientations of the 15N chemical shift tensor of [1-15N]-2'-deoxyguanosine were determined from a polycrystalline sample using the two-dimensional PISEMA experiment. The magnitudes of the principal values of the 15N chemical shift tensor of the N1 nitrogen of [1-15N]-2'-deoxyguanosine were found to be sigma11 = 54 ppm, sigma22 = 148 ppm, and sigma33 = 201 ppm with respect to (15NH4)2SO4 in aqueous solution. Comparisons of experimental and simulated two-dimensional powder pattern spectra show that sigma33N is approximately collinear with the N-H bond. The tensor orientation of sigma33N for N1 of [1-15N]-2'-deoxyguanosine is similar to the values obtained for the side chain residues of 15Nepsilon1-tryptophan and 15Npi-histidine even though the magnitudes differ significantly.     

Magnitudes and Orientations of the N Chemical Shift Tensor of [1-N]-2′-Deoxyguanosine Determined on a Polycrystalline Sample by Two-Dimensional Solid-State NMR Spectroscopy

The magnitudes and orientations of the ¹⁵N chemical shift tensor of [1-¹⁵N]-2′-deoxyguanosine were determined from a polycrystalline sample using the two-dimensional PISEMA experiment. The magnitudes of the principal values of the ¹⁵N chemical shift tensor of the N1 nitrogen of [1-¹⁵N]-2′-deoxyguanosine were found to be ς₁₁ = 54 ppm, ς₂₂ = 148 ppm, and ς₃₃ = 201 ppm with respect to (¹⁵NH₄)₂SO₄ in aqueous solution. Comparisons of experimental and simulated two-dimensional powder pattern spectra show that ς_33N is approximately collinear with the N–H bond. The tensor orientation of ς_33N for N1 of [1-¹⁵N]-2′-deoxyguanosine is similar to the values obtained for the side chain residues of ¹⁵N_ε1-tryptophan and ¹⁵N_π-histidine even though the magnitudes differ significantly.     

Germania nanocrystals in Modified Chemical Vapour Deposition

The Modified Chemical Vapour Deposition process for fabrication of silica-based optical fibres is used to generate nanoscale soot particles which are deposited on a substrate by thermophoresis and then sintered and collapsed into a preform from which optical fibre can be drawn. To increase the refractive index of the fibre core silica and germania soots are often generated together and co-deposited. The silica soot is invariably amorphous in character but for certain configurations of the preform lathe it has been found that germania soot particles may be crystalline. A systematic study has identified parameters controlling germania crystallinity in soot nanoparticles and transition from crystalline germania nanoparticles to glassy germania has been observed. The implications of possible retention of germania nanocrystals in preform and fibre are discussed with regard to fibre quality and optical performance.