A Review of Polyolefin-Insulation Materials in High Voltage Transmission; From Electronic Structures to Final Products.

This review focuses on the use of polyolefins in high-voltage direct-current (HVDC) cables and capacitors. A short description of the latest evolution and current use of HVDC cables and capacitors is first provided, followed by the basics of electric insulation and capacitor functions. Methods to determine dielectric properties are described, including charge transport, space charges, resistivity, dielectric loss, and breakdown strength. The semicrystalline structure of polyethylene and isotactic polypropylene is described, and the way it relates to the dielectric properties is discussed. A significant part of the review is devoted to describing the state of art of the modeling and prediction of electric or dielectric properties of polyolefins with consideration of both atomistic and continuum approaches. Furthermore, the effects of the purity of the materials and the presence of nanoparticles are presented, and the review ends with the sustainability aspects of these materials. In summary, the effective use of modeling in combination with experimental work is described as an important route toward understanding and designing the next generations of materials for electrical insulation in high-voltage transmission.

Mass spectrometry-based metabolomics for the elucidation of alkaloid biosynthesis and function in invasive Vincetoxicum rossicum populations.

The genus Vincetoxicum includes a couple of highly invasive vines in North America that threaten biodiversity and challenge land management strategies. Vincetoxicum species are known to produce bioactive phenanthroindolizidine alkaloids that might play a role in the invasiveness of these plants via chemical interactions with other organisms. Untargeted, high-resolution mass spectrometry-based metabolomics approaches were used to explore specialized metabolism in Vincetoxicum plants collected from invaded sites in Ontario, Canada. All metabolites corresponding to alkaloids in lab and field samples of V. rossicum and V. nigrum were identified, which collectively contained 25 different alkaloidal features. The biosynthesis of these alkaloids was investigated by the incorporation of the stable isotope-labelled phenylalanine precursor providing a basis for an updated biosynthetic pathway accounting for the rapid generation of chemical diversity in invasive Vincetoxicum. Aqueous extracts of aerial Vincetoxicum rossicum foliage had phytotoxic activity against seedlings of several species, resulting in identification of tylophorine as a phytotoxin; tylophorine and 14 other alkaloids from Vincetoxicum accumulated in soils associated with full-sun and a high-density of V. rossicum. Using desorption-electrospray ionization mass spectrometry, 15 alkaloids were found to accumulate at wounded sites of V. rossicum leaves, a chemical cocktail that would be encountered by feeding herbivores. Understanding the specialized metabolism of V. rossicum provides insight into the roles and influences of phenanthroindolizidine alkaloids in ecological systems and enables potential, natural product-based approaches for the control of invasive Vincetoxicum and other weedy species.

Coarse-Grained Model for Prediction of Hole Mobility in Polyethylene.

Electrical conductivity measurements of polyethylene indicate that the semicrystalline structure and morphology influence the conductivity. To include this effect in atomistic charge transport simulations, models that explicitly or implicitly take morphology into account are required. In the literature, charge transport simulations of amorphous polyethylene have been successfully performed using short oligomers to represent the polymer. However, a more realistic representation of the polymer structure is desired, requiring the development of fast and efficient charge transport algorithms that can handle large molecular systems through coarse-graining. Here, such a model for charge transport simulations in polyethylene is presented. Quantum chemistry calculations were used to define six segmentation rules on how to divide a polymer chain into shorter segments representing localized molecular orbitals. Applying the rules to amorphous systems yields distributions of segments with mode and median segment lengths relatively close to the persistence length of polyethylene. In an initial test, the segments of an amorphous polyethylene were used as hopping sites in kinetic Monte Carlo (KMC) simulations, which yielded simulated hole mobilities that were within the experimental range. The activation energy of the simulated system was lower compared to the experimental values reported in the literature. A conclusion may be that the experimental result can only be explained by a model containing chemical defects that generate deep traps.

Rapid entry to phenanthroindolizidine alkaloids via an acid-catalysed acyliminium ion-electrocyclization cascade.

A rapid total synthesis of seco-phenanthroindolizidine alkaloids was achieved involving a one-pot acid catalyzed deprotection- condensation-electrocyclization strategy. This synthetic route provided a concise synthesis of (±)-seco-antofine and (±)-septicine in only 4 steps with an overall yield of 22% and 17%, respectively.

Interest of nailing associated with the Masquelet technique in reconstruction of bone defect.

INTRODUCTION: The Masquelet technique based on induced membrane is performed in two stages, first with generally an external fixator which is more and more relayed by an internal fixator. The aim of this study is to assess the results of stabilization by using intramedullary nailing from the first stage. PATIENTS AND METHODS: Nine patients were treated for a bone defect concerning 8 femurs and one tibia. The mean size of bone defect was 9.25 cm. It was secondary to a fracture (6 case) with bone defect and two septic and aseptic pseudarthrosis. In all cases the nailing was performed at the first stage of Masquelet. Prior to cement delivery, the site was thoroughly cleaned with iterative excisions as needed. Blood count control, normal CRP and negative culture were required before cement delivery. The cement was placed around the nail and encased the bony extremity. In the second stage, after removal of the cement, the defect was fulfilled by a mixture of cortico-cancellous autogenous graft taken from the iliac crest and phosphocalcic bone substitute. The nail was not changed in any patient. In post operative the mobilization of the above and underlying joints was immediate. RESULTS: No sepsis was detected before the second time. Early weight bearing was allowed on average at the end of the 2 nd month. Total bearing without support was allowed at a mean of 5.5 months. All patients have consolidated. One patient had a shortening of 2.35 cm. The mean follow-up was 46.1 months. The average period to effective return to work was 21 months. CONCLUSION: The nailing performed at the first stage of the induced membrane technique (IMT) gives good results. This modification does not seem to increase the risk of infection. These good results deserve to be confirmed by other studies to confirm the interests of associating nailing to IMT from the first stage.