Development And Characterization Of Normoxic Polyhydroxyethylacrylate (Nphea) Gel Dosimeters Using Magnetic Resonanc Imaging (Mri) Clinical Scanner

Polymer gel dosimeter is a three dimensional (3D) polymer gel system for recording radiation dose distribution in radiotherapy treatment planning. The dosimeter is based on polymerization of copolymers induced locally by free radicals, the products of water radiolysis. Interaction of free radicals with the monomer and crosslinker causes a breakage of double C=C bonds into single C-C bonds, leading to copolymerization between the two copolymers to form high density insoluble polymer in gelatin matrix and is normally achieved by purging nitrogen into the system to remove oxygen during preparation. In this work, new type of polymer dosimeter, i.e. the ‘normoxic’ polymer gels, is synthesized by adding oxygen scavenger to remove oxygen. The dosimeter is based on polyhydroxyethylacrylate (nPHEA) gels containing 2-4% (w/w) 2-hydroxythylacrylate (HEA) monomer, 2-4% (w/w) bisacrylamide (BIS) comonomer, 3-5% (w/w) gelatin, and 87-93% (w/w) water in normal atmospheric condition. The polymer gel phantoms were irradiated with beam doses up to 30 Gy using 60Co teletherapy -ray source at a constant dose rate of 0.22 Gy/min. The polymerization of nPHEA dosimeters was evaluated by means of magnetic resonance imaging (MRI) clinical scanner, which produced 3D optical density distribution and registered as MRI films. The gray scale of MRI images was measured using an optical densitometer. The optical density of the polymer gels was found to increase with increasing of absorbed dose and decreased with the increase of depth inside the phantom. The optical density was then converted to absorb dose by a mathematical relationship obtained from the experiment. The dose-depth maps for nPHEA gels were obtained for different concentrations of co-monomers, gelatin and at different beam doses. The results indicated that dose decreases of with decreasing of depth and gelatin concentration and increases with increasing of co-monomer concentrations. Finally the cross beam dose-depth map has been acquired by irradiating nPHEA phantom from two (3 cm x 3 cm) square -ray beams of 14 Gy and 25 Gy which perpendicular to each other. The results showed the distribution of 3D dose-depth profile that decreased with increasing depth and lower beam dose. One region of high dose distribution in particular was seen in the overlapped beams, which in the actual clinical practices, it may represent a cancer volume that to be inactivated with higher dose than the surrounding healthy non-cancer tissues

MyHouse : un système de négociation multi-critères dans le commerce électronique, appliqué au domaine du courtage immobilier

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

The Mechanical Behavior Variation of Nickel - Titanium Orthodontic Wires in Different Fluoride Mouthwash

In this study, an orthodontic arch wire of Ni-Ti alloy made by Germany in four different mouthwashes contain fluoride was investigated in mechanical behavior. This research focused on the mechanical behavior changes in different mouthwashes. The Mouthwashes were chosen from most popular one in Iran including Oral-B, Gum, and Behsa Mouthwash. The wires after 3 month in touch with mouthwashes were studied and the result was presented. The result show that the lowest power to reshape the wire, is for the wire in Crest case (3). The maximum power assigns to wire in Behsa case (1). Also, the shortest treatment period is for wire in Behsa mouthwash case (1) with 0.087 Nm strain energy and the maximum duration of therapy is related to case (3) Crest mouthwash with 0.039 Nm. Moreover, the wires in Oral-b (0.095 Nm) has the lowest and Gum mouthwash (0.140 Nm) has the highest energy intake. The energy absorbed by the wires in Behsa and Crest is in the middle. Finally, it is proposed that patient could use all mouthwash but based on their condition, one product will be useful

Thermoluminescence properties of nanostructured calcium borate as a sensitive radiation dosimeter for high radiation doses

The crystalline calcium tetraborate (CaB4O7) nanoparticles were synthesized using a combination of facile co-precipitation and thermal treatment. The synthesized phosphor nanoparticles were found to possess a monoclinic nanostructure of particle size of about 8 nm. The thermoluminescence (TL) glow curve of the nanoparticles shows a single peak centred at about 150°C. The TL nanophosphor revealed an excellent dosimetric response with a respectable linearity in the dose range of 0.05 to 1000 Gy, which is wider than its counterparts prepared by non nanosynthesis methods. They exhibited good luminescence efficiency and wide range linearity, suggesting the present phosphor nanoparticles may be considered as a suitable candidate for the dosimetric applications

Structural and optical properties of PVP-capped nanocrystalline ZnxCd1−xS solid solutions

Nanocrystalline ZnxCd1−xS solid solutions were prepared in a microwave-assisted hydrothermal process with gradient distribution of components (x = 0.1, 0.3, 0.5, 0.7, and 0.9). The growth of the cubic-structured quantum dots was observed for all component stoichiometries with the crystallite size between 4.5 and 5.7 nm. The obvious peak shifts have been found in the XRD patterns and the lattice parameters showed linear variation with x increasing. The evolution of the optical properties of obtained solid solutions including absorption and photoemission was also monitored in detail. The solid solutions show a considerable shift in the nanoparticle optical absorption edge from 482 to 343 nm with the increasing of Zn fraction. The band gaps of the solid solutions were estimated to be between 2.94 and 3.40 eV and the position of conduction band was shifted toward more negative potential with x increasing. The photoluminescence spectra showed a broad blue-green emission spreading up to 600 nm with emergence of three dominant peaks belong to sulfur, zinc, and cadmium vacancies

Facile synthesis of ZnS/CdS and CdS/ZnS core-shell nanoparticles using microwave irradiation and their optical properties

ZnS/CdS and CdS/ZnS core shell nanoparticles with tunable shell thickness were synthesized via a two steps route under microwave irradiation. In the first step core nanoparticles were prepared using polyol method, and in the second step capping process of shells were performed at moderate temperature by choosing ethanol as a solvent. The thickness of the shells was controlled by adjusting the concentration of core nanoparticles and shell precursors. The structural and chemical characterizations were performed using X-ray diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy which provide direct evidence for shell growth. The structures of ZnS/CdS and CdS/ZnS core shell nanoparticles were similar to the cubic and hexagonal core structures, respectively. The optical properties of obtained core shell nanoparticles were characterized using UV-Visible and photoluminescence spectroscopy. The absorption edge of ZnS/CdS core shells shows a red shift compared to ZnS (core) while for CdS/ZnS, the absorption edge shows a blue shift compare to CdS (core) owing to the size effect and the potential-well effect. The emission peaks of ZnS/CdS and CdS/ZnS core shell nanoparticles in the range of 400-650 nm are from sulfur, zinc and cadmium vacancy defects and created surface states at ZnS/CdS and CdS/ZnS interfaces

High coercivity sized controlled cobalt–gold core–shell nano-crystals prepared by reverse microemulsion

Size-controlled cobalt–gold core–shell nanoparticles were synthesized via the reverse-micelle microemulsion method. In order to control the size of the nanoparticles, the nucleation and growth process were performed within a confined space by adjusting the water to surfactant ratio of reverse micelles solution during synthesis. The crystallinity percentage and percentage of phases presented in Co–Au core–shell nanoparticles were calculated using X-ray diffraction data. The results from transmission electron microscopy provide direct evidence for core–shell structure nanomaterials. Magnetic properties of the samples were investigated using a vibrating sample magnetometer. The as-prepared samples showed significant coercivity at room temperature. The intrinsic blocking temperature was experimentally deduced from zero-field-cooled warmed (ZFC-W) curves by a simple method without employing an external magnetic field. The B-field dependence temperature data of Co–Au nanoparticles exhibited an intrinsic blocking temperature at 45 K. Annealing these samples at 400 °C caused an increase in particle size, crystallinity percentage and further enhanced their magnetic properties

Enhancement of visible light photocatalytic activity of ZnS and CdS nanoparticles based on organic and inorganic coating

Coating of ZnS and CdS nanoparticles with organic and inorganic materials can extend their light absorption in the visible region and their stability against photo-corrosion. Such materials could emerge as excellent photocatalysts for the elimination of pollutants from aqueous media using solar energy. In this study, PVP (polyvinyl pyrrolidone)-capped ZnS and CdS nanoparticles, ZnS/CdS and CdS/ZnS core shell nanoparticles were synthesized by microwave irradiation method and characterized using different techniques. The XRD patterns exhibited cubic and hexagonal structures for coated ZnS and CdS nanoparticles, respectively. Morphological evaluation of TEM images showed that the nanoparticles are generally spherical in shape. The UV–visible spectra confirmed a shift in the band gap of coated nanoparticles to longer or shorter wavelengths due to size and potential-well effects. The photocatalytic activity of nanoparticles toward dye degradation under visible light was found to be improved after coating. PVP-capped ZnS and CdS exhibited an enhancement in the initial methylene blue degradation efficiency by a factor of about 1.3. ZnS nanoparticles coated by CdS displayed the initial efficiency 3.2 times higher than bare ZnS. The maximum dye removal was obtained in presence of CdS/ZnS core shells which is 1.4 times more efficient than bare CdS

Photocatalytic degradation of methylene blue under visible light using PVP-capped ZnS and CdS nanoparticles

Photocatalysis based on semiconductor quantum dots which utilize the solar energy can be used for the elimination of pollutants from aqueous media and applied for water purification. Degradation of dyes is a standard method to check the photocatalytic activity of any type of photocatalyst. In this paper polyvinyl pyrrolidone (PVP)-capped ZnS and CdS nanoparticles were prepared by a simple microwave irradiation method and studied in detail for their photocatalytic activity in visible range. The obtained nanoparticles were characterized by XRD, TEM, UV–Vis and EDX. The prepared PVP-capped ZnS and CdS nanoparticles have average sizes of ∼5.1 and 18.3 nm with cubic and hexagonal crystalline structures, respectively. PVP capped CdS nanoparticles exhibited a unique property of optical absorption in visible region with a wave length below than 460 nm followed by a clear long tail up to 700 nm and showed excellent activity toward degradation of dye under visible light illumination. The photocatalytic activity of PVP-capped CdS nanoparticles was found to be improved by mixing with appropriate amount of PVP-capped ZnS nanoprticles. From the study of variation in weight percentages of PVP-capped ZnS nanoparticles, the physical mixture with 20% of PVP-capped ZnS nanoparticles was found to be very efficient for degradation of methylene blue. In this case the degradation efficiency after 6 h illumination was about 81%

Growth and characterization of La0.7Na0.3MnO3 thin films prepared by pulsed laser deposition on different substrates

Perovskite manganite La0.7Na0.3MnO3 thin films were directly grown on MgO (1 0 0), Si (1 0 0) and glass substrates by pulsed laser deposition. From the XRD patterns, the films are found polycrystalline single-phases rhombohedral. The surface appears porous and cauliflower-like morphology for all LNMO films. LNMO films deposited on the glass substrate were presented smooth morphologies of the top surfaces as compared with other films. The highest magnetoresistance value obtained was −18.86% for LNMO/MgO films at 80 K in a 1 T magnetic field. Phase transition temperature is 221 K for LNMO/Cg, 214 K for LNMO/Si and 144 K for films deposited on MgO substrates. The films exhibit ferromagnetic transition at a temperature around 286 K for LNMO/MgO, 304 K for LNMO/Si and 292 K for LNMO/Cg thin film. The Curie temperature of LNMO films deposited on the glass substrate, 292 K is the highest value that is reported in literature for LNMO films deposited on low-cost amorphous substrates