On convex permutations

A selection of points drawn from a convex polygon, no two with the same vertical or horizontal coordinate, yields a permutation in a canonical fashion. We characterise and enumerate those permutations which arise in this manner and exhibit some interesting structural properties of the permutation class they form. We conclude with a permutation analogue of the celebrated Happy Ending Problem.     

Clean seeding for flow visualization and velocimetry measurements

Flow visualization, particle image velocimetry (PIV), and laser Doppler velocimetry (LDV) are among the most useful tools available for experimental aerodynamics studies. Implementation of these techniques, however, requires that seed material be introduced into the flow. The undesirable qualities of the seeding material often prevent the use of flow visualization and velocimetry techniques in many test environments. This is particularly true for large-scale, closed-circuit tunnels where facility operators must weigh the risks of facility contamination, sensor damage, and safety concerns that might result from the introduction of seed particles. Identification of a practical clean seeding material that minimizes or eliminates these concerns would enable flow visualization and velocimetry techniques to be deployed in these facilities. Here, we demonstrate two seeding systems that have the potential to provide such a solution. The first system is a new concept which uses liquid carbon dioxide that can be made to form discrete particles as it expands from a high-pressure tank. PIV measurements are demonstrated in several flows, including supersonic and subsonic tunnels, using these residue-free seed particles. The second system utilizes a combination of steam and liquid nitrogen to produce an aerosol or fog that serves as flow seeding. Water- or steam-based seeding has been previously demonstrated for flow visualization in subsonic tunnels; here however, we utilize this seed material for PIV and LDV measurements as well as for flow visualization in a large supersonic tunnel.     

Thermally-Induced Extrusion of Sulfur Dioxide from Allyl Alkyl Sulfones. Use of the Rearrangement for the Synthesis of Dihydrojasmone

For some time we have been interested in the mechanistic and potential synthetic applications of the thermal transformation illustrated in equation (1)^1.     

A method for crack sizing using Laser Doppler Vibrometer measurements of Surface Acoustic Waves

The goal of non-destructive testing (NDT) is to determine the position and size of structural defects, in order to measure the quality and evaluate the safety of building materials. Most NDT techniques are rather complex, however, requiring specialized knowledge. In this article, we introduce an experimental method for crack detection that uses Surface Acoustic Waves (SAWs) and optical measurements. The method is tested on a steel beam engraved with slots of known depth. A simple model to determine the cracks size is also proposed. At the end of the article, we describe a possible application: fatigue crack sizing on a damaged slat track. This technique represents a first step toward a better understanding of the crack growth, especially in its early stages (preferably when the cracks can still be repaired) and when it is possible to assume a linear propagation of the crack front. The ultimate goal of this research program is to develop a useful method of monitoring aircraft components during fatigue testing.     

Core-shell Molecular Imprinted Polymer Colloids

Molecular imprinted core-shell colloidal polymer particles have been prepared in which the shells were formed, in aqueous media, in the presence of organic templates. The most selective system involved the use of an unsaturated alkyl phosphate as the electrostatic binding motif. Systems that were able to selectively differentiate between caffeine and theophylline and the Gly-Gly sequence in tripeptides are described. Radiotracing experiments showed that all of the caffeine template could be removed following extraction.     

Fluorinated Copolymer PCPDTBT with Enhanced Open-Circuit Voltage and Reduced Recombination for Highly Efficient Polymer Solar Cells

A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC(70)BM compared to the well-known low-band-gap polymer PCPDTBT. Fluorination lowers the polymer HOMO level, resulting in high open-circuit voltages well exceeding 0.7 V. Optical spectroscopy and morphological studies with energy-resolved transmission electron microscopy reveal that the fluorinated polymer aggregates more strongly in pristine and blended layers, with a smaller amount of additives needed to achieve optimum device performance. Time-delayed collection field and charge extraction by linearly increasing voltage are used to gain insight into the effect of fluorination on the field dependence of free charge-carrier generation and recombination. F-PCPDTBT is shown to exhibit a significantly weaker field dependence of free charge-carrier generation combined with an overall larger amount of free charges, meaning that geminate recombination is greatly reduced. Additionally, a 3-fold reduction in non-geminate recombination is measured compared to optimized PCPDTBT blends. As a consequence of reduced non-geminate recombination, the performance of optimized blends of fluorinated PCPDTBT with PC(70)BM is largely determined by the field dependence of free-carrier generation, and this field dependence is considerably weaker compared to that of blends comprising the non-fluorinated polymer. For these optimized blends, a short-circuit current of 14 mA/cm(2), an open-circuit voltage of 0.74 V, and a fill factor of 58% are achieved, giving a highest energy conversion efficiency of 6.16%. The superior device performance and the low band-gap render this new polymer highly promising for the construction of efficient polymer-based tandem solar cells.     

Development of an extraction method for the determination of prostaglandins in biological tissue samples using liquid chromatography–tandem mass spectrometry: Application to gonads of Atlantic cod (Gadus morhua)

A simple extraction method for the analysis of PGE₂ and PGF_2α in gonad samples from Atlantic cod and further quantification by using liquid chromatography–tandem mass spectrometry is proposed. The evaluation of the best solvent extraction conditions and the analytical performance parameters are reported. The method was highly selective for both prostaglandins and the calibration curves, based on the internal standard method, were linear between 5 and 1000 ng mL⁻¹ for PGE₂ and PGF_2α, with limits of detection of 1 ng mL⁻¹ and 1.5 ng mL⁻¹ and recovery values of 99.999 ± 0.002 and 99.967 ± 0.023 respectively. The homogenization of samples using liquid nitrogen combined with the developed extraction protocol can be implemented in different types of biological tissues.