Time filter

Source Type

Varennes, Canada

Dreval M.,University of Saskatchewan | Dreval M.,National Science Center Kharkov Institute of Physics and Technology | Xiao C.,University of Saskatchewan | Elgriw S.,University of Saskatchewan | And 3 more authors.
Review of Scientific Instruments | Year: 2011

A technique is presented for determining the radial location of the rotating magnetic islands in the STOR-M tokamak by use of soft x-ray (SXR) detector arrays. The location is determined by examining the difference in the integrated SXR emission intensities through two adjacent lines of sight. A model for calculating dependence of the line integrated SXR emission intensity on the radius, the mode numbers and the magnetic island geometry, has been developed. The SXR difference signal shows phase inversion when the impact parameter of the line of sight sweeps across the magnetic islands. Experimentally, the difference SXR signals significantly reduce noise and suppress the influence of background plasma fluctuations through common mode rejection when a dominant mode exists in the STOR-M tokamak. The radial locations of the m 2 magnetic islands have been determined under several experimental conditions in the STOR-M discharges. With the decrease in the tokamak discharge current and thus the increase of the safety factor at the edge, the radial location of the m 2 magnetic islands has been found to move radially inward. © 2011 American Institute of Physics.

Levasseur O.,University of Montreal | Stafford L.,University of Montreal | Gherardi N.,National Polytechnic Institute of Toulouse | Gherardi N.,CNRS LAPLACE Lab | And 6 more authors.
Plasma Processes and Polymers | Year: 2012

This work examines the functionalization of sugar maple (Acer saccharum) and black spruce (Picea mariana) wood surfaces using an atmospheric-pressure dielectric barrier discharge in He and He/HMDSO (hexamethyldisiloxane) gas mixtures. Wood samples were placed on one of the electrodes and the plasma was sustained by applying a 3.5 kV peak-to-peak voltage at 12 kHz. Analysis of the discharge stability through current-voltage (I-V) characteristics revealed a filamentary behaviour, in sharp contrast with the homogeneous He discharge obtained with a glass sample. Optical emission spectroscopy performed near the wood vicinity revealed strong N2 and N2 + emissions, suggesting that wood outgassing plays an important role in the evolution of the discharge regime. Analysis of the surface wettability through water contact angle (WCA) measurements indicated that freshly sanded wood samples treated in He/HMDSO plasmas became more hydrophobic with WCAs in the 120°-140° range depending on treatment time and wood species. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy measurements on samples exposed to He/HMDSO plasmas revealed the deposition of hydrophobic Si(CH3)3-O-Si(CH3)2, Si(CH3)3 and Si(CH3)2 functional groups as well as an increase of the CH-to-OH band intensity ratio. For relatively thick coatings, the WCA following natural aging under uncontrolled conditions remained constant at 132° ± 3° which highlights the stability of the plasma-deposited thin films, a very promising result for structural and decorative outdoor applications. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA.

Pregent J.,University of Montreal | Vandsburger L.,University of Montreal | Blanchard V.,Pulp and Paper Research Institute of Canada | Blanchet P.,Laval University | And 3 more authors.
Cellulose | Year: 2015

The effect of O2 addition in the gas feed of an open-to-air N2–O2 dielectric barrier discharge (DBD) on the surface modification of sugar maple hardwood samples is reported. After treatment by N2–O2 plasma, an increase of the contact angle with water and a decrease of the contact angle with diiodomethane was observed. X-ray photoelectron spectroscopy and Fourier-transform infra-red analyses further reveal a decrease of the O/C as well as increase of the C=O peak and surface aromaticity. When O2 is added to the nominally pure N2 DBD, the discharge transits from a homogeneous regime to a filamentary regime with increased dissipated power and neutral gas temperature. As a result, surface modification by N2–O2 plasmas becomes similar to those occurring under a low-temperature heat treatment of wood surfaces. In such conditions, a mechanism involving the thermally-activated deacetylation and depolymerisation of hemicelluloses and cross-linking between lignin and furfural and hydroxylmethylfurfural, leading to the increase of wood hydrophobicity is proposed. © 2015, Springer Science+Business Media Dordrecht.

Busnel F.,Laval University | Blanchard V.,19 rue Franquet | Pregent J.,University of Montreal | Stafford L.,University of Montreal | And 3 more authors.
Journal of Adhesion Science and Technology | Year: 2010

This work examines the adhesion properties of sugar maple (Acer saccharum) and black spruce (Picea mariana) wood surfaces following their exposure to a dielectric barrier discharge at atmospheric pressure. Freshly sanded wood samples were treated in Ar, O2, N2 and CO 2-containing plasmas and then coated with a waterborne urethane/acrylate coating. In the case of black spruce wood, pull-off tests showed adhesion improvement up to 35% after exposure to a N2/O 2 (1:2) plasma for 1 s. For the same exposure time, adhesion improvements on sugar maple wood up to ∼25% were obtained in Ar/O 2 (1:1) and CO2/N2 (1:1) plasma mixtures. Analysis of the wettability with water contact angle measurements indicate that the experimental conditions leading to adhesion improvement are those producing more hydrophobic wood surfaces. In the case of sugar maple samples, X-ray photoelectron spectroscopy investigations of the near-surface chemical composition indicate an increase of the O/C ratio due to the formation of functional groups after exposure to oxygen-containing plasmas. It is believed that a combination of structural change (induced by UV radiation, metastable particles impingement, or both) and chemical change due to surface oxidation is responsible for the observed surface modification of black spruce and sugar maple wood samples. © 2010 Koninklijke Brill NV, Leiden.

Yan C.,University of Quebec | Yan C.,McGill University | Nikolova L.,University of Quebec | Dadvand A.,University of Quebec | And 6 more authors.
Advanced Materials | Year: 2010

(Figure Presented) Multiple NaNbO3 nanoplates are created within Nb2O5 nanotubes forming a unique class of heterostructure nanotubes combining ferroelectric and semiconducting nanomaterials. Local piezoelectric studies on NaNbO3 nanoplates show clear ferroelectric behavior (see figure), while the semiconductive properties of the host Nb 2O5 nanotubes allows for switching of electrical conductivity by an external electric field. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA,.

Discover hidden collaborations