Dissertations / Theses on the topic 'Irradiative'
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1
OKA, TOHRU, TOSHIO KANEDA, MINORU UEDA, and YASUNORI SUMI. "Effects of Irradiation on Grafted Skin : Vascular Changes after Irradiation." Nagoya University School of Medicine, 1985. http://hdl.handle.net/2237/17473.
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Misner, Scottie, Carol Curtis, and Evelyn Whitmer. "Irradiation of Food." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2008. http://hdl.handle.net/10150/146430.
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2 pp.Revised version of 1999 title by Meer and Misner
Food irradiation is the treatment of food by a certain type of intense energy known as ionizing radiation. This involves exposing bulk or packaged food to carefully controlled amounts of energy. Food does not come in contact with radioactive material. The publication discusses the technology of food irradiation including; the energy source, effect on foods, identifying treated foods, environmental concerns and approved uses in the U.S.
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Auvray, Marie-Hélène. "Endommagement sous irradiation de l'aluminate de lithium γ-LiALO₂." Paris 11, 1987. http://www.theses.fr/1987PA112381.
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Cette étude est motivée par l'application potentielle de ce matériau comme couverture tritigene dans les réacteurs de fusion. Elle complète ainsi les études déjà effectuées sur la caractérisation et les mécanismes de production des défauts dans d'autres cristaux ioniques. Irradiation par des projectiles varies (électrons, ions he(+), protons, photons x et gamma) et étude par rpe et absorption optique (détection des défauts ponctuels crées) et par microscopie électronique par transmission (analyse des échantillons avant irradiation et observation des défauts étendus produits par irradiation)
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Aitkaliyeva, Assel. "Irradiation Stability of Carbon Nanotubes." [College Station, Tex. : Texas A&M University, 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-08-3251.
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Dubé, Frédéric. "Spiral irradiation in stereotactic radiosurgery." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0016/MQ55049.pdf.
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Dubé, Frédéric 1973. "Spiral irradiation in stereotactic radiosurgery." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29884.
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The aim of stereotactic radiosurgery is to deliver a high and uniform radiation dose to the target volume and a minimized dose to the surrounding healthy tissue. Various linac-based radiosurgical techniques are used clinically: multiple non-coplanar converging arcs, dynamic arc rotation, and conical rotation. The techniques differ in their beam distribution over the patient's head.A study of the beam distribution characteristics for the clinical linac-based radiosurgical techniques is presented. Two spiral linac-based radiosurgical techniques are developed: the uniform dose-rate spiral irradiation and the dose-rate-weighted spiral irradiation. Both exhibit the same spiraling beam entry trace over the patient's head; however, they differ in their beam distribution along the spiral. The dose-rate-weighted spiral irradiation provides a uniform beam distribution over the 2pi solid angle available in radiosurgery.
The currently existing techniques and the spiral techniques are then compared using the cumulative dose-volume histogram (CDVH) tools available with the McGill Treatment Planning System (MPS). The dose-rate-weighted spiral technique leads to lower dose inhomogeneities within the target volume and better dose conformity within the target. Moreover, it also encompasses smaller volumes of tissue at all isodose levels with larger differences at low isodose levels. A conclusion is reached that the dose-rate-weighted spiral irradiation technique offers interesting advantages over the currently used clinical linac-based techniques.
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Shaibani, S. J. "Electron irradiation damage of spinal." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371580.
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Gelbart, W. "Bulk liquid-metal irradiation system." Helmholtz-Zentrum Dresden - Rossendorf, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-165893.
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Introduction
Low melting point metals are often encapsulated in a hermetic container, irradiated and the container transferred to hot-cell for material removal and processing. An important process of this kind is the production of 82Sr from rubidium (melting point: 39.5 °C.)
This new concept departures completely form the encapsulated targets approach and allows an almost continues production by the irradiation of the bulk metal. As well, eliminated is the target transfer. By placing the target material dissolution chamber right in the target station, only the dissolution product is pumped to the hotcell for further processing.
Material and Methods
Some of the disadvantages of the encapsulated target are:
1. Complicated transfer system that is ex-pensive to install, slow and prone to failures.
2. Complex and expensive encapsulation procedure.
3. Loss of production time during the lengthy target changing.
4. Capsule geometry is constrained by the encapsulating process and transfer demands compromising heat transfer and beam power.
To avoid the difficulties of liquid metal handling, metal salts are often used instead (rubidium chloride is one example). This creates other problems and limits the beam currents and production yields.
In the system described, the liquid metal is transferred (by gravity) from a bulk container to an irradiation chamber. The chamber, made out of nickel-plated silver, holds the correct quantity of rubidium for one irradiation run. Because of the geometry of the chamber and the efficient cooling, up to 40KW of beam power can be delivered to the target. The chamber is equipped with thermocouples and a liquid-metal level detector and is entirely of welded/brazed construction. The alloy foil that forms the beam window is electron-beam welded to the chamber front ring.
At the end of irradiation the irradiated liquid metal is gravity fed into a reaction chamber situ-ated below the irradiation chamber, and a new load of fresh rubidium released into the irradia-tion chamber. The liquid-metal transfer and the irradiation components are shown on FIG. 1, and the sectional view on FIG. 2.
Appropriate chemicals (n-butanol in the case of rubidium) are delivered to the reaction chamber and the irradiated metal dissolved. The liquid dissolution product is transferred back to the hotcell. Since all steps of the reaction involve liquids, only small diameter tubes connect the target station with the hotcell. The transfer is fast and simple.
The bulk liquid-metal storage container can be constructed to hold enough material for 10 or more runs. When empty, it is replaced with a pre-loaded one. The container is connected to the target system with one coupling and the exchange takes a short time. A robotic bottle exchange can be implemented if desired.
The station is equipped with its own vacuum system, beam diagnostic (consisting of a four-sector mask) and a collimation. The target chamber and each of the beam intercepting components are electrically insulated to allow beam current monitoring.
Constructed entirely out of metal and ceramic the target core assembly does not suffer from radiation damage. The use of aluminum, silver and alumina reduce component activation.
Results and Conclusion
A large part of the station design is based on the well proven construction of high current solid target system and is using the same, or similar components.
Test was performed to optimize the liquid-metal transfer and the chamber filling with the correct volume, while leaving some room for expansion.
A process for niobium coating of sliver is investi-gated. Niobium is known to provide good corro-sion resistance against liquid metals.
Thermal modelling of the target and flow analysis of the cooling geometry is under way.
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Booi, Mlamli. "Ore sorting using microwave irradiation." Master's thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/8336.
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Bibliography: leaves 99-101.Automatic ore sorting machines are in common use in the mining industry. These machines generally separate valuable mineral-bearing rocks from waste rocks. At the Premier Diamond Mine in South Africa kimberlite, a diamond-bearing rock is separated from gabbro which is a waste rock. Work had been conducted previously in the Department of Electrical Engineering at the University of Cape Town to find a viable method for discriminating between gabbro and kimberlite. A technique using microwave irradiation attenuation was successful when using parallel-sided smooth-surfaced rocks. This technique used linearly polarized square antennas at 35GHz. Problems were experienced, however, with irregu1arly shaped rock s. The aim of the present study was therefore to deve1op a technique which will sort irregularly shaped rocks and eliminate the problems associated with them.
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Mercer, Sean R. "Rock differentiation using microwave irradiation." Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/9638.
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Includes bibliographical references.This project arose as a result of inefficiencies in the diamond recovery process at Premier Mine. A considerable amount of barren waste rock, gabbro, is mined along with the diamond bearing kimberlite. No automated method exists for separating the kimberlite from the waste rock and a device was required to effect ore sorting on a rock by rock basis. Experimentation with a microwave oven indicated that samples of kimberlite were more attenuative than samples of gabbro. The possibility of using microwave heating for rock differentiation was investigated but was impractical to implement. A study of low power microwave attenuation and reflection measurements was undertaken. Reflection measurements were found to be impractical due to the similar amounts of reflected signal from the different rock types. Microwave signal attenuation through rock samples was studied over a broad frequency spectrum. A detectable difference in signal attenuation was found through the gabbro and kimberlite. The difference in signal attenuation increased with increasing frequency. Different techniques to implement signal attenuation measurements through rock samples were investigated. The passing of rock samples through waveguide structures was found to be impractical in this application. Microwave signal attenuation measurements were successful when rock samples were placed between a transmitting and a receiving antenna. Equipment was designed and constructed with an operating frequency of 35GHz chosen due to the small antenna aperture area and the large attenuation difference at this frequency. Static measurements with this equipment revealed the problems with signal scattering and reflection from some irregularly shaped samples of low loss gabbro. The importance of these phenomenon could only be gauged from dynamic measurements. Dynamic measurements were performed using a laboratory test system with a conveyor belt capable of moving at speeds of up to 5 m/s. It was found that 93% of the kimberlite could be correctly detected whilst rejecting 67% of the gabbro. The system functioned satisfactorily and led to the filing of several patents.
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Réjasse, Barbara. "Biocatalyse sous irradiation micro-ondes." La Rochelle, 2005. http://www.theses.fr/2005LAROS141.
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Dans cette étude, nous avons utilisé l'irradiation micro-ondes comme source d'énergie pour réaliser différentes biosynthèses catalysées par des β-galactosidases ou la lipase B de Candida antarctica. L'influence de ce mode de chauffage alternatif sur l'activité et la stabilité enzymatiques est étudiée. Trois types de milieux réactionnels (aqueux fortement concentré en substrat, sans solvant et avec solvant organique) sont testés pour la mise en œuvre de biocatalyseurs sous irradiation micro-ondes. Dans chaque cas, le profil réactionnel obtenu est comparé à celui observé sous chauffage classique par convection, à la même température macroscopique. En milieux aqueux, nous avons étudié la biosynthèse de galacto-oligosaccharides à 40°C par transgalactosidation. La vitesse initiale de la réaction, son équilibre, ainsi que la réaction d'hydrolyse secondaire sont identiques sous irradiation micro-ondes et chauffage classique. En milieu organique, l'alcoolyse du butyrate d'éthyle par le butanol, catalysée par la lipase B de Candida antarctica, sous forme libre et immobilisée, est étudiée en système sans solvant et dans différents solvants de logP compris entre -0,15 et 3,29. En système sans solvant, de 40 à 100°C, le mode de chauffage n'a pas d'influence sur la vitesse initiale et l'équilibre de la réaction d'alcoolyse. Dans le système avec solvant, la vitesse initiale de la réaction augmente d'un facteur 1,8 sous irradiation micro-ondes, tandis que le même équilibre réactionnel est obtenu sous les deux modes de chauffage. Le facteur d'accélération de la réaction, sous irradiation, semble ne pas dépendre de la polarité du solvant utilisé. La stabilité de la lipase, en stockage dans le butanol ou le butyrate d'éthyle, est influencée par le mode de chauffage. Le processus d'inactivation enzymatique peut être ralenti ou accéléré dans le champ électromagnétique, en fonction de la température d'incubationIn this study, we have used the microwave irradiation as energy source to carry out various biosynthesis catalysed by β-galactosidases or Candida antarctica lipase B. The influence of this alternative heating mode on the enzymatic activity and stability is studied. Three types of reactional media (aqueous highly concentrated in substrates, without solvent and with organic solvent) are tested for the implementation of biocatalysts under microwave irradiation. In each case, the reactional profile obtained is compared with that observed under traditional heating (convection), at the same macroscopic temperature. In aqueous medium, a transgalactosidation reaction is studied at 40°C. The initial rate of reaction, the reactional equilibrium and the rate of secondary hydrolysis are identical under both heating modes. In organic medium, the alcoholysis of ethyl butyrate and butanol catalyzed by Candida antarctica lipase B (free and immobilized form) is studied in a solvent free system and in various solvents (logP ranging between -0,15 and 3,29). In solvent free system, the heating mode doesn't have any effect on the initial rate and reactional equilibrium of the alcoholysis, from 40 to 100°C. In solvent system, the initial rate of the reaction increases by an 1,8-factor under microwave irradiation, while identical reactional equilibrium is obtained under both heating modes. The acceleration factor of the reaction under irradiation seems not to depend on the solvent polarity. The lipase stability in storage in butanol or ethyl butyrate is influenced by the heating mode. The process of enzymatic inactivation can be slowed down or accelerated in the electromagnetic field, according to the temperature of incubation
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Giamarchi, Philippe. "Contribution à l'analyse des produits de radiolyse des lipides : applications en agro-alimentaire." Aix-Marseille 3, 1993. http://www.theses.fr/1993AIX30024.
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L'etude des composes de radiolyse des lipides presente un interet particulier du fait qu'elle peut conduire a la detection et a la quantification de l'ionisation des produits (alimentaires ou non) riches en lipides. Ce travail porte sur l'identification et le dosage des hydrocarbures radioinduits; ces composes sont analyses grace a un systeme d'espace de tete dynamique suivi d'une chromatographie en phase gazeuse. La mise au point des conditions d'analyse a ete realisee en utilisant la methodologie de la recherche experimentale. La conservation des hydrocarbures radioinduits a ete etudie en s'attachant notamment a l'ajout d'antioxydants. Une etude des risques d'interference en particulier lors de la thermolyse a ete menee. Enfin, on a pu montrer que leur teneur augmente lineairement avec la dose d'ionisation. Ce travail a constitue la base de l'elaboration d'un test permettant d'une part d'identifier les produits ionises, d'autre part de quantifier la dose d'ionisation. La limite de detection atteinte dans le cas des huiles vegetales est de 0,1 kgy. Enfin, cette technique a ete appliquee sur l'avocat, pour lequel la limite de detection est de 0,5 kgy
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Ono, Yuka. "Dosimetric advantages afforded by a new irradiation technique, Dynamic WaveArc, used for accelerated partial breast irradiation." Kyoto University, 2020. http://hdl.handle.net/2433/253145.
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Quentin, Alexis. "Modifications structurales de spinelles sous irradiation." Phd thesis, Université de Caen, 2010. http://tel.archives-ouvertes.fr/tel-00549397.
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Ce travail concerne l'étude de matériaux de structure spinelle sous irradiations. Pour cela, des échantillons de ZnAl2O4 polycristallins et MgAl2O4 monocristallins ont été irradiés par différents ions lourds de hautes énergies. Les échantillons de ZnAl2O4 ont été étudiés par microscopie électronique en transmission ainsi que par diffraction des rayons X en incidence rasante et analyse Rietveld. Les échantillons de MgAl2O4 ont été étudiés en spectroscopie optique. Les résultats concernent principalement l'amorphisation et les modifications de la structure cristalline de ZnAl2O4, notamment l'inversion. Nous avons pu déterminer un seuil en pouvoir d'arrêt pour l'amorphisation, compris entre 11 keV/nm et 12 keV/nm, ainsi que la cinétique d'amorphisation, qui est une cinétique à multiples impacts. Nous avons étudiés par MET l'évolution de la fraction amorphe et avons mis en évidence un phénomène de nanopatterning. Concernant l'inversion, nous avons pu déterminer qu'elle se faisait via un processus d'impact unique, et que sa valeur à saturation n'atteignait pas celle d'une répartition aléatoire des cations. L'inversion et l'amorphisation possèdent des seuils de déclenchement en pouvoir d'arrêt différents, bien que très proches. L'amorphisation semble cependant être conditionnée par un préendommagement du matériau qui se traduit également par une inversion.
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Bauer, Cletus P. "Electron irradiation n type cadmium telluride." Thesis, Monterey, California. Naval Postgraduate School, 1985. http://hdl.handle.net/10945/21306.
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Ogilvy-Stuart, Amanda Lesley. "Endocrine sequelae of irradiation in childhood." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296367.
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Titapiwatanakun, V. "Pharmaceutical applications of CO2 laser irradiation." Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1474179/.
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In the pharmaceutical development pipeline, most drugs are poorly soluble; therefore, it is important to tackle this problem by applying novel drug delivery systems or alter the drug substances with either chemical or physical modification such as amorphous formation, co-crystal formation or solid dispersion system to yield better dissolution, absorption and thus therapeutic efficacy. Applying technologies from other fields to develop such systems could be advantageous. Carbon dioxide (CO2) laser irradiation causes rapid melting and vapourization of materials through the absorption of infrared energy from a laser beam. The aim of this work was to investigate the potential pharmaceutical applications of CO2 laser irradiation in several areas including drug delivery systems, drug substances and mixtures of drug and polymer. CO2 laser irradiation was successfully utilized for three main pharmaceutical systems. Firstly, modifying drug release of irradiated enteric coated tablets (Eudragit®L100-55, L30D-55 and HPMCAS-MF) targeting to the duodenum gave rise to both fast and delayed release in pH 5.6 phosphate buffer resembling the duodenum. These changes were caused by pore formation and the change in wettability on the surface of the irradiated coat. Cast films were used to examine the physicochemical and mechanical changes and were shown to have different mechanical properties, contact angles and wettability upon high irradiation. Secondly, a proof-of-concept study of pharmaceutical co-crystal production upon irradiation at certain energy (S50P50) from a mixture of specific stoichiometric ratio of dry powders was presented through rapid melting, sublimation and vapour crystallization. Furthermore, the CO2 laser can induce the physical conversion to amorphous state of the drug-alone system (classic indomethacin) and to many physical states of the various ratios of the drug (paracetamol) and polymer (polyvinylpyrrolidone K 30) mixtures upon rapid heating process. These were clearly confirmed by a range of analytical techniques and physical stability studies. The effect of underlying process settings, namely, laser power, scanning speed, irradiation area, resolution, working distance and scale-up on production were performed.
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Schuller, Bradley W. "Selective irradiation of the vascular endothelium." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/44787.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007."September 2007."
Includes bibliographical references.
We developed a unique methodology to selectively irradiate the vascular endothelium in vivo to better understand the role of vascular damage in causing normal tissue radiation side-effects.The relationship between vascular endothelial cell apoptosis and intestinal crypt stem cell death was evaluated using uniform whole-body and selective vascular irradiation techniques. Mice received whole-body epithermal neutron beam irradiation. Additional dose was selectively targeted to endothelial cells from the short-ranged (5-9 [mu]m) particles released from neutron capture reactions in 10B confined to the blood by incorporation into 70-90 nm-diameter liposomes. Mice also received uniform photon doses above and below the threshold for death from the gastrointestinal (GI) syndrome. When plotted versus neutron beam dose, the crypt microcolony assay showed the same dose response for both the neutron beam-only and neutron beam plus boronated liposome groups. The added dose selectively delivered to the microvasculature did not cause any additional crypt loss. Jejunal cross-sections were prepared 4 hrs after irradiation and stained with TUNEL to observe and score apoptotic cells in the villus lamina propria. To uniquely identify the type of cell undergoing apoptosis in the lamina propria, intestinal specimens from various mice in the TUNEL studies were sectioned and stained with Meca-32 to identify endothelial cells and caspase-3 to identify apoptotic cells and visualized using dual-fluorescence microscopy. The TUNEL data showed a low level (~2 apoptotic cells per villus) of apoptosis in the lamina propria for both the uniform (photon or neutron) and selective vascular irradiation conditions that was independent of the administered dose.
(cont.) The dual-fluorescence studies indicated that most apoptotic bodies in the lamina propria were not endothelial cells but, rather, apoptotic leukocytes. These data demonstrate that there is no causal relationship between vascular endothelial cell apoptosis and crypt stem cell death in the mouse small intestine.
by Bradley W. Schuller.
Ph.D.
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Holtom, Philip Derek. "Irradiation studies of astrophysical ice analogues." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1444790/.
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In this thesis the formation of molecular species in cold icy mantles, typical of those in the interstellar medium (ISM) has been studied. The construction of an ultra high vacuum system for the formation and containment of these astrophysical ice analogues is described. The method of preparation of these ices is detailed and analysis methodologies are discussed. VUV spectra of molecular ices (e.g. SO2, CH3NH2, OCS) measured on the UV1 beam line of the Astrid Synchrotron facility at the University of Aarhus in Denmark, are presented. Molecular synthesis (e.g. CO3, CO, H2CO3) induced by ion irradiated CO2/H 2O ices using facilities at Queens University Belfast are also reported. In particular this thesis focuses on the irradiation studies of the binary ice mixture of Methylamine (CH3NH2) and Carbon Dioxide (CO2). The results of irradiation of CH3NH2 and CO2 binary ice mixtures by ultraviolet photons, and electrons are presented. The apparent production of the amino acid - glycine - in our irradiated samples is discussed together with possible production processes.
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Sobie, Cameron. "Prediction of irradiation hardening in metals." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54963.
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The purpose of this thesis is to improve predictions of irradiation hardening in metals with a focus on coarse-graining via meso-scale simulations. Increasing hardness and decreasing in ductility in nuclear reactor pressure vessel steel is the limiting factor of nuclear reactor life, and accurately predicting reactor life is of the utmost importance for the safe operation of nuclear facilities. This is an inherently multi-scale problem with primary damage occurring at the atomic scale and its effects propagating across ten orders of magnitude in length and time scale to changes in macroscopic material properties, which must be reflected in its methods of prediction.
To achieve this goal, this thesis develops two novel approaches to simulate the motion of dislocations in irradiated alpha-iron. First, a dislocation dynamics simulation coarse-graining insight from atomistic dislocation-defect simulations is used to guide the selection of proposed constitutive models. Several studies investigating the effect of size distribution show that the mean defect size can be used with the selected models to predict material hardening without a complex treatment for the defect size distribution. The hardening effect of the commonly observed defect types are found independently and a superposition principle is proposed for materials with both defect types. Second, a link to transition state theory and thermally activated reactions is established using a new method augmenting a discrete dislocation dynamics simulations with the nudged elastic band method to characterise the minimum energy pathways of dislocation reactions. This development enables calculations of activation energy for dislocation events using a continuum method as well as the numerical calculations of dislocation attempt frequency. The thesis concludes with an extension to the analysis of coarse-graining unit events to large scale dislocation-obstacle bypass phenomena.
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Hanif, Imran. "Ion irradiation modification of silicon nanowires." Thesis, University of Huddersfield, 2017. http://eprints.hud.ac.uk/id/eprint/32630/.
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Ion irradiation modification of silicon nanowires has been explored in-situ using the Microscope and Ion Accelerator for Materials Investigations (MIAMI) facility at the University of Huddersfield. Ion irradiation experiments were designed using the Stopping and Range of Ions in Matter (SRIM) Monte Carlo computer code. A multislice SRIM method was developed to estimate the damage and ion implantation in a nanowires geometry and a code was developed to incorporate SRIM into MatLab. In-situ Transmission Electron Microscopy (TEM) has been used to explore the ion-beam-induced bending of silicon nanowires under different irradiation conditions and the underlying mechanisms which drive nanowire bending have been identified. Furthermore, a tipping point for direction reversal of bending under different irradiation conditions has been identified. Recrystallisation of silicon nanowires was also investigated using thermal annealing. The effects of 7 keV Xe+ ions on silicon nanowires have been investigated under industrial processing conditions. Structural and morphological changes of silicon nanowires have been observed. These include nanowire bending, amorphisation, bubble formation and sputtering. The depth of damage has also been measured experimentally and was compared with the predictive damage using SRIM. In order to calculate the temperature along a nanowire during an in-situ TEM heating experiment, the relevant parameters have been found from the literature which will be used to set up a finite element model. Atomic Force Microscopy (AFM) was used to measure the surface roughness of silicon nanowires and molybdenum grids. Other parameters of interest include the Hamaker’s constant for the Van der Waals forces as well as the Young’s modulus, thermal conductivity and specific heat capacity of silicon nanowires and the ultra-thin oxide layer on their surface.
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Sibuyi, Praise. "Irradiation induced effects on 6h-SIC." University of the Western Cape, 2012. http://hdl.handle.net/11394/8467.
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Philosophiae Doctor - PhDThe framework agreement in the year 2000 by the international community to launch Generation IV program with 10 nations, to develop safe and reliable nuclear reactors gave rise to the increased interest in the studies of SiC and the effect of different irradiations on solids. Silicon carbide is a preferred candidate used in harsh environments due to its excellent properties such as high chemical stability and strong mechanical strength. The PBMR technology promises to be the safest of all nuclear technology that have been developed before. SiC has been considered one candidate material being used in the fabrication of pebble bed fuel cell. Its outstanding physical and chemical properties even at high temperatures render it a material of choice for the future nuclear industry as whole and PBMR in particular. Due to the hostile environment created during the normal reactor operation, some of these excellent properties are compromised. In order to use this material in such conditions, it should have at least a near perfect crystal lattice to prevent defects that could compromise its strength and performance. A proper knowledge of the behavior of radiation-induced defects in SiC is vital. During irradiation, a disordered crystal lattice occurs, resulting in the production of defects in the lattice. These defects lead to the degradation of these excellent properties of a particular material. This thesis investigates the effects of various radiation effects to 6H-SiC. We have investigated the effects of radiation induced damages to SiC, with a description of the beds and the importance of the stability of the SiC-C interface upon the effects of radiations (y-rays, hot neutrons). The irradiated samples of 6H-SiC have been studied with various spectroscopic and structural characterization methods. The surface sensitive techniques such as Raman spectroscopy, UV-Vis, Photoluminescence and Atomic Force Microscopy will be employed in several complimentary ways to probe the effect of irradiation on SiC. The obtained results are discussed in details.
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Rana, Aman. "Optimizing Weed Management via Microwave Irradiation." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/75115.
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One potential alternative to chemical weed control is the use of microwave radiation, a particular form of indirect thermal weeding. Absorption of microwave radiation causes water molecules within the tissue to oscillate, thereby converting electromagnetic energy into heat. This technique is rapid, versatile and effective, as the electromagnetic waves heat the plant tissue and destroy cellular integrity. The objective of this research was to evaluate the potential use of dielectric heating for weed management. Ten weed species representing monocots and dicots were selected for this study: southern crabgrass, dallisgrass, yellow nutsedge, fragrant flatsedge, false green kyllinga, common ragweed, field bindweed, henbit, white clover, and pitted morningglory. There was a lag or warm up period between energizing the magnetron and actual microwave radiation production. To eliminate the gap between electric power supplied to magnetron and actual microwave radiation produced, a conveyer was used. Overall injury to grasses, sedges and broadleaf weeds was higher at each dose when weeds were treated by microwave radiation while moving on a conveyer in comparison to being stationary. Grasses showed slightly more tolerance to microwave treatments in comparison to broadleaf weeds. Older weeds (8 to 10 weeks old) showed more tolerance to microwave treatments in comparison to younger weed plants (4 to 6 weeks old). Microwave radiation was able to control a range of weed species, although larger weeds were more likely to regrow after treatment. Ambient temperature had a significant effect on injuries caused by microwave radiation to target weeds, with control increasing as the air temperature increased. Weed control using microwave radiation required more energy when weeds were treated at 13 C compared to 35 C. More energy was needed at lower air temperatures to raise the plant canopy temperature from ambient levels to beyond the biological limit. Microwave radiation at lower doses caused greater injury to common chickweed and yellow woodsorrel than bermudagrass, suggesting the potential for selective weed control in certain situations. A custom built microwave applicator provided similar control of emerged weeds as the contact herbicides diquat and acetic acid.Ph. D.
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Torchy, Séverine. "Transfert d'hydrogène sous irradiation micro-ondes." Lille 1, 2000. http://www.theses.fr/2000LIL10069.
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Cette étude concerne les réactions de transfert d'hydrogène sous irradiation micro-ondes, utilisant comme agents de transfert des molécules organiques telles que l'acide formique, les dihydropyridines et les alcoolates d'aluminium. L'aspect physique de l'irradiation micro-ondes, ses répercussions sur la matière, et les applications possibles en synthèse organique sont résumés. Une deuxième partie étudie la N-méthylation (la N,N-diméthylation) d'amines secondaires (primaires) par le méthanal en présence d'acide formique. La réaction est généralement réalisée sans solvant, un net effet micro-ondes est mis en évidence. Cet accès aisé à des amines tertiaires conduit ensuite à étudier le comportement des sels d'ammonium qui en dérivent dans les conditions de transposition de Stevens ou Sommelet-Hauser : l'irradiation micro-ondes accélère ces réarrangements. Les deux réactions quaternarisation-transposition peuvent s'opérer en une seule étape (réaction tandem). Une quatrième partie concerne la synthèse de dihydropyridines et leur utilisation comme agents de réduction d'alcènes désactivés. Les dihydropyridines non substituées en 4 se prêtent aisément à un transfert d'hydrogène : les pyridines et les alcanes résultants sont préparés en une seule étape. Les deux derniers chapîtres concernent l'utilisation d'alcoolates d'aluminium dans la réduction des dérivés carbonylés (5ʿ partie) et la réaction inverse, l'oxydation d'alcools (6ʿ partie). La réduction s'opère aisément avec des résultats très satisfaisants. L'oxydation est plus délicate à mettre en œuvre.
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AKAMATSU, JOUSSET MARIELLE. "Evolution structurale d'alliages ferritiques sous irradiation." Paris 11, 1994. http://www.theses.fr/1994PA112007.
Full textAbstract:
Nous avons etudie l'evolution, sous l'effet de l'irradiation, de la microstructure et des proprietes mecaniques d'alliages ferritiques modele (fe-cu) et d'aciers de cuve de reacteur nucleaire a eau pressurisee (chooz a). Trois traitements de precipitation sont compares: vieillissement thermique a 500c, irradiation aux electrons (3mev, 290c) et irradiation aux neutrons (290c). L'utilisation conjointe de la sonde atomique et de la diffusion des neutrons aux petits angles a permis d'obtenir les caracteristiques (taille, densite numerique, composition) des precipites formes a l'echelle nanometrique, en fonction du temps ou de la fluence. Dans les alliages fe-cu (0 a 1,4% poids) irradies, les precipites ne sont pas constitues de cuivre pur (comme le prevoirait le diagramme de phase), mais contiennent une forte proportion de fer et de lacunes. Les mesures de durete sous faible charge montrent un net durcissement du a ces precipites. Les irradiations conduisent a un durcissement superieur a celui du au vieillissement thermique, du fait de la creation de nombreux defauts ponctuels. Nous avons essaye d'analyser nos resultats dans les termes du modele durcissement par effet de module de russel et brown. Nos tentatives d'evaluation non destructive par mesure du bruit barkhausen revelent simplement que les precipites formes par irradiation sont vraisemblablement trop petits pour etre detectes. Dans l'acier de cuve, l'irradiation aux neutrons en service a conduit a la formation de nuages d'atomes de ni, mn, si et cu au sein de la matrice de fer
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Quentin, Alexis. "Modifications structurales de spinelle sous irradiation." Caen, 2010. http://www.theses.fr/2010CAEN2059.
Full textAbstract:
Ce travail concerne l'étude de matériaux de structure spinelle sous irradiations. Pour cela, des échantillons de ZnAl2O4 polycristallins et MgAl2O4 monocristallins ont été irradiés par différents ions lourds de hautes énergies. Les échantillons de ZnAl2O4 ont été étudiés par microscopie électronique en transmission ainsi que par diffraction des rayons X en incidence rasante et analyse Rietveld. Les échantillons de MgAl2O4 ont été étudiés en spectroscopie optique. Les résultats concernent principalement l'amorphisation et les modifications de la structure cristalline de ZnAl2O4, notamment l'inversion. Nous avons pu déterminer un seuil en pouvoir d'arrêt pour l'amorphisation, compris entre 11 keV/nm et 12 keV/nm, ainsi que la cinétique d'amorphisation, qui est une cinétique à multiples impacts. Nous avons étudiés par MET l’évolution de la fraction amorphe et avons mis en évidence un phénomène de nanopatterning. Concernant l'inversion, nous avons pu déterminer qu'elle se faisait via un processus d’impact unique, et que sa valeur à saturation n'atteignait pas celle d'une répartition aléatoire des cations. L'inversion et l'amorphisation possèdent des seuils de déclenchement en pouvoir d'arrêt différents, bien que très proches. L’amorphisation semble cependant être conditionnée par un pré-endommagement du matériau qui se traduit également par une inversionThis work is devoted to the study of spinel structure materials under radiation. For that purpose, samples of polycrystalline ZnAl2O4 and monocrystalline MgAl2O4 were irradiated by different heavy ions with different energies. Samples of ZnAl2O4 were studied par electron transmission microscopy, and by grazing incidence X-Ray diffraction and Rietveld analysis. Samples of MgAl2O4 were studied by optical spectroscopy. Most of the results concern amorphisation and crystalline structure modification of ZnAl2O4 especially the inversion. We were able to determine a stopping power threshold for amorphisation, between 11 keV/nm and 12 keV/nm, and also the amorphisation process, which is a multiple impacts process. We studied the evolution of the amorphous phase by TEM and showed a nanopatterning phenomenon. Concerning the inversion, we determined that it did happen by a single impact process, and the saturation value did not reach the random cation distribution value. Inversion and amorphisation have different, but close, stopping power threshold. However, amorphisation seems to be conditioned by a predamage of the material which consists in inversion
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Hu, Rong. "Irradiation effects on Fe-Cr alloys." Thesis, University of Oxford, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.560928.
Full textAbstract:
Ferritic chromium steels are important structural materials for future nuclear fission and fusion reactors due to their advantages over traditional austenitic steels, including low swelling rates, better thermal fatigue resistance, and lower thermal expansion coefficients. Radiation-induced segregation or depletion (RIS/RID) of solute atoms at grain boundaries is considered to be a potentially significant phenomenon for structural materials because of its potentially detrimental role in affecting microstructure and furthermore mechanical properties. However, the behaviour of Cr at grain boundaries in ferritic steels is not well understood. Both segregation and depletion of Cr at grain boundary under irradiation have been previously observed and no clear dependency on irradiation condition or alloy type has been presented. Furthermore, ferritic alloys are known to undergo hardening and embrittlement after thermal aging in the temperature range of 300-550DC and this phenomenon is related with a and a' phase separation occurring in the solid solution. However the low temperature a-a' miscibility gap in the currently used phase diagram is extrapolated from high temperature results and conflicts with many experimental observations. To understand the Cr behaviour at gram boundaries in ferritic steels under irradiation, a systematic approach combining SEM/EBSD, FIB specimen preparation and APT analysis has been developed and successfully applied to a Fe- 15.2at%Cr to investigate the effect of pre-irradiation chemistry, grain boundary misorientation, impurities, irradiation damage, irradiation depth, and other possible factors to get a better understanding of RIS/RID phenomena. Both low sigma boundaries and randomly selected high angle boundaries have been investigated in detail. Systematic differences between the behaviour of different classes of boundaries had been observed, and the operating mechanisms are also discussed in this thesis. The maximum separation method has been applied on APT data to study the C- enriched clusters and Cr-enriched clusters, which were not directly visible on the atom maps. The composition of the Cr-enriched clusters was consistent with a' phase and the irradiation was found to accelerate the nucleation rather than the growth of these clusters. Such results provided important information in re- determining the a-a' phase boundary.
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Le, Gac Alexandre. "Comportement sous irradiation des verres d'aluminosilicate." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX047/document.
Full textAbstract:
La compréhension des effets d’irradiation dans les verres d’oxyde est importante dans le domaine du conditionnement des déchets nucléaire et requière l’évaluation du rôle des formateurs de réseau, principalement le silicium, le bore et l’aluminium, mais aussi du rôle des éléments alcalins et alcalino-terreux qui peuvent agir en tant que modificateurs de réseau ou compensateurs de charge. Les verres d’aluminoborosilicates ont été très étudiés et le rôle des changements de coordinence du bore sur l’évolution structurale du verre sous irradiation a été souligné. Cependant, il n’y a que peu d’études sur les verres d’aluminosilicates et presque qu’aucune information sur l’influence de l’aluminium et de ses compensateurs de charge sur l’évolution du réseau sous irradiation. Ce travail de thèse a donc pour objectif de déterminer les effets de la teneur en aluminium et du type de compensateurs de charge (ici les ions sodium et calcium) sur l’évolution de la structure des verres d’aluminosilicates sous irradiation. Afin de comprendre les différents phénomènes dans les verres d’oxyde complexes, 13 verres simplifiés, composés d’oxydes de SiO2, Al2O3, Na2O et CaO, ont été élaborés. Ainsi, l’influence des rapports Na2O/CaO et Al2O3/SiO2 et de la teneur en Al2O3 ont été investigués. Pour simuler les désintégrations alpha et comparer les dommages électronique et balistique, des irradiations externes aux ions He2+ d’énergie 5 MeV et aux ions Au4+ d’énergie 7 MeV ont été réalisées sur les verres. Des irradiations aux électrons ont également été faites afin d’obtenir des échantillons irradiés en volume par des collisions électroniques à faible pouvoir d’arrêtThe understanding of radiation effects in oxide glasses is important in nuclear waste conditioning field and requires the evaluation of the role of the glass formers, mainly silicon, boron and aluminum, but also of the alkali and alkali-earth elements that can act either as modifier elements or charge compensators. Aluminoborosilicate glasses were highly studied and the role of boron coordination changes on structural evolution under irradiation was highlighted. However, there are only few studies on aluminosilicate glasses and almost no information about the influence of aluminum and its charge compensators on the glassy network evolution under irradiation. The goal of this work is therefore to determine the effects of aluminum content and type of charge compensators (here, Na and Ca cations) on the aluminosilicate glass structure evolution under irradiation. To understand the different phenomena in complex oxide glasses, 13 simplified glasses, composed of SiO2, Al2O3, Na2O and CaO oxides, were elaborated. Hence, the influence of Na2O/CaO and Al2O3/SiO2 ratios, and Al2O3 content, were investigated. To simulate alpha decays and compare electronic and ballistic damage, external irradiations at room temperature with 5 MeV He2+ and 7 MeV Au4+ were performed on glasses. 2.5 MeV electron irradiations were also done to obtain bulk samples irradiated by electronic collisions at low stopping power
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Pellegrino, Stéphanie. "Irradiation aux ions des carbures ZrC et TiC. Effets des pertes d'énergie électronique et nucléaire." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS018/document.
Full textAbstract:
Cette étude est orientée sur les céramiques réfractaires des métaux de transition, comme le carbure de titane et de zirconium, envisagées pour leurs caractéristiques de résistance en conditions extrêmes. Ces céramiques seraient soumises à différentes sources d'irradiation (les neutrons, les produits de fission, les désintégrations alpha) dans les futurs réacteurs de génération IV. Les rayonnements rencontrés en réacteur peuvent être simulés par des irradiations externes à l'aide d'accélérateurs de particules, en utilisant des ions variés dans une large gamme d'énergie. Ces instruments permettent de reproduire en conditions contrôlées l'endommagement subi par des les matériaux internes aux centrales nucléaires.Dans un tel contexte radiatif, deux processus majeurs gouvernent l'endommagement des matériaux: les collisions nucléaires induites par les irradiations avec des ions de faible énergie (comme les noyaux de recul) et les excitations électroniques intervenant dans les irradiations avec des ions de grande énergie (comme les produits de fission). La prédominance de l'un ou de l'autre de ces processus est reliée à la masse et à l'énergie de la particule accélérée. Pour comprendre la contribution de chaque effet dans les mécanismes d'endommagement des structures cristallines soumises à des irradiations, nous avons simulé des rayonnements impliquant, d'une part, des ions de basse énergie, i.e. de quelques MeV et, d'autre part, des ions de grande énergie, i.e. de quelques centaines de MeV. Les principaux objectifs de ce travail ont été: (i) d'étudier le comportement de ces deux carbures sous irradiation, (ii) de déterminer les modifications structurales, chimiques et mécaniques induites par les effets nucléaires et électroniques, (iii) de comprendre les mécanismes d'endommagement dans ces carbures dans le régime nucléaire et (iv) d'essayer d'expliquer les résultats expérimentaux par les calculs obtenus en simulation.Pour cela, différentes techniques de caractérisation ont été combinées afin d'expliquer le scénario de ces carbures sous irradiation avec comme référence, le carbure de silicium SiC très étudié par le passé. Ces techniques complémentaires sont: la spectrométrie de rétrodiffusion de Rutherford en mode canalisé (RBS-C), la diffraction des rayons X (DRX), la spectroscopie Raman, la microscopie électronique en transmission (MET) et la nanoindentation. La combinaison de ces techniques expérimentales ainsi que la simulation a permis de conforter nos résultats et les différentes hypothèses formulées. Nous avons pu établir ainsi un scénario pour ces deux types de carbures TiC et ZrC sous irradiation aux ionsThis study is focused on the ceramic refractory transition metals, such as titanium carbide and zirconium envisaged to their strength characteristics under extreme conditions. These ceramics are subject to various sources of radiation (neutrons, fission products, the alpha decays) in future generation reactors IV. Radiation encountered in the reactor can be simulated by external irradiation with particle accelerators, using various ions in a wide energy range. These instruments can reproduce in controlled conditions damage suffered by nuclear materials.In such radiative context, two major processes govern damages into the materials: nuclear collisions induced by irradiation with low energy ions (like the recoil nuclei) and electronic excitations involved in irradiation with high-energy ions (such as fission products). The predominance of one of these processes is connected to the mass and energy of the accelerated particle. To understand the contribution of each effect in the damage mechanisms of crystal structures subjected to irradiation, we simulated radiation involving, on the one hand, low energy ions, i.e. a few MeV and, secondly, high energy ions, i.e. a few hundred MeV. The main objectives of this work were: (i) to study the behavior of these two carbides under irradiation, (ii) determine the structural, chemical and mechanical changes induced by nuclear and electronic effects, (iii) understand the damage mechanisms in these carbides in the nuclear regime and (iv) to try to explain the experimental results obtained by simulation calculations.For this, various characterization techniques were combined to explain the scenario of these carbides under irradiation as a reference, the silicon carbide SiC extensively studied in the past. These additional techniques are: Rutherford Backscattering Spectrometry in channeling mode (RBS-C), the X-ray diffraction (XRD), Raman spectroscopy, Transmission Electron Microscopy (TEM) and nanoindentation. The combination of these experimental techniques and simulation helped to consolidate our results and various assumptions. We were able to establish a scenario for these two types of carbides TiC and ZrC under ion irradiation
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Dahl, Erik Monroe. "Single-Walled Carbon Nanotube Response to Neutron and Gamma Irradiation." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/50856.
Full textAbstract:
The unique electronic properties of single-walled carbon nanotubes (SWNTs) have sparked interest for using such nanomaterials in the nuclear industry and within radiation detection devices. To explore the application of SWNTs in the nuclear industry, it was first deemed necessary to study how SWNTs respond to the two main types of radiation occurring in nuclear environments, neutrons and gamma rays. SWNT samples were irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory with neutrons and gamma rays at incremented lengths of time allowing for multiple fluence intensities to be received by the samples. After irradiation, Raman spectroscopy was used to monitor the damage incurred from neutron and gamma irradiation. It was found that disorder within the SWNT lattice network increased with increasing irradiation intensity. The results indicated that the gamma irradiation was causing the majority of the damage with little to no damage caused by the neutron irradiation. Further investigation showed that the non-linearity of the disorder increase with increasing irradiation intensity was typical of sample doping instead of the expected particle impacts. It was concluded that the gamma irradiation was generating dopants within the SWNTs by the process of water radiolysis. Water vapor trapped between the SWNT film layer and the substrate that the film layer was placed on was identified as the source of the sample dopants. Although unexpected, the results from this experiment have provided insight into a potential gamma radiation detection technique using SWNTs that has never been considered until now.
Master of Science
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Just, Guillaume. "Caractérisation et modélisation des mémoires Flash embarquées destinées aux applications faible consommation et à forte contrainte de fiabilité." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4716/document.
Full textAbstract:
De nombreuses applications industrielles spécifiques dans les secteurs tels que l'automobile, le médical et le spatial, requièrent un très haut niveau de fiabilité. Ce type d'applications fonctionnant sous des contraintes sévères (haute température, corrosion, vibration, radiations,…) impose aux industriels des spécifications particulières en termes de fiabilité et de consommation d'énergie. Dans ce contexte, les travaux menés ont pour objectif d'étudier la fiabilité des mémoires Flash embarquées pour des applications faible consommation et à forte contrainte de fiabilité. Après une introduction orientée sur les deux volets d'étude que sont la caractérisation électrique et le test de mémoires non volatiles, un modèle physique capable de modéliser le courant de SILC a été développé. Cet outil permet de répondre à la problématique de perturbations en lecture (read disturb) et donne aux designers et technologues un moyen d'estimer le taux de défaillance de cellules mémoires en fonction de paramètres physiques, géométriques et électriques ainsi que des moyens d'action afin de minimiser ce phénomène indésirable. La fiabilité (oxyde tunnel, endurance) et les performances (consommation énergétique) de la cellule Flash sont ensuite étudiées en explorant les variations de paramètres du procédé de fabrication et des conditions électriques de fonctionnement. Enfin, une étude originale menée en temps réel sur plus de 15 mois est consacrée à la fiabilité en rétention des mémoires Flash soumises aux effets des particules radiatives présentes dans l'environnement naturel terrestreMany specific applications used in automotive, medical and spatial activity domains, require a very high level of reliability. These kinds of applications, working under severe constraints (high temperature, corrosion, vibration, radiations…) challenge memory manufacturers and impose them particular specifications in terms of reliability and energy consumption. In this context, work presented in this thesis aim at studying embedded Flash memories reliability for low power and high reliability applications. After an introduction oriented on areas of electrical characterizations and Test of non-volatile memories, a physical model of SILC leakage current is developed. This tool is used to answer to disturbs problematic and gives to designers and technologists a way to estimate the failure rate of memory cells according to physical, geometrical and electrical parameters, giving leads to minimize this unwanted phenomenon. Reliability (tunnel oxide, cell endurance) and performances (energy consumption) of Flash memory cell are then studied exploring process parameters variations and electrical conditions optimizations. Finally, an original real-time experiment over more than 15 months is focused on Flash memories retention reliability due to irradiative particles effects of natural terrestrial environment
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Jutier, Frédéric. "Influence de l'auto-irradiation sur la supraconductivité de composés à base de plutonium." Paris 11, 2006. http://www.theses.fr/2006PA112115.
Full textAbstract:
Bien que le plutonium (Pu) soit plus connu pour ses propriétés nucléaires, il est également un métal fascinant dont les électrons 5f se situent à la frontière entre un caractère itinérant et localisé. Ce comportement unique dans le tableau périodique des éléments positionne le Pu métal à un croisement dans les propriétés électroniques. La découverte récente de la supraconductivité dans PuCoGa5 et PuRhGa5 est une nouvelle preuve directe de la complexité des propriétés électroniques du plutonium. Les valeurs élevées de la température critique et du deuxième champ critique semble indiquer l'existence d'une troisième classe de supraconducteurs, transitoire entre les composés fermions lourds à base d'uranium et de cérium, et les supraconducteurs à haute température critique à base de cuprates. Les grandes valeurs des paramètres critiques associées à une densité de courant élevée donneraient à ces nouveaux matériaux un potentiel prometteur pour de futures applications technologiques, si ce n'était le caractère extrêmement radiotoxique des composés à base de plutonium. L'intérêt des composés PuCoGa5 et PuRhGa5 est la décroissance alpha du plutonium qui constitue alors une source continue d'irradiation in situ. Le vieillissement de ces composés aura donc un impact sur les paramètres critiques de la supraconductivité. Ce travail a donc porté sur l'étude par résistivité électrique et aimantation de l'évolution des paramètres de la supraconductivité en fonction du vieillissement des échantillons, pour en déduire l'influence des " impuretés " et des défauts sur leur comportement supraconducteur et déterminé des indications éventuelles d'un caractère non conventionnelAlthough plutonium (Pu) is most known for its nuclear properties, it is also a fascinating metal whose 5f electrons are at the threshold between itinerancy and localization. This unique behaviour in the periodic table makes Pu metal being at the crossover in electronic properties. The recent discovery of superconductivity in PuCoGa5 and PuRhGa5 is a new direct evidence of plutonium's electronic properties complexity. The high values of the critical temperature and the upper critical field seem to point to the existence of a third class of superconductor, transitional between uranium- and cerium-based heavy fermion systems, and the high-Tc copper oxides. If it were not for the toxicity hazards associated with plutonium compounds, and their high critical parameters together with a high critical current, would make these materials of promising potential for technological applications. The advantage of the PuCoGa5 and PuRhGa5 compounds is the alpha radioactivity of plutonium which constitutes a continuous in situ source of irradiation. The ageing of these compounds will have thus an impact on the critical parameters (Tc, Hc2, Jc). This work is based on the study by electrical resistivity and magnetisation of the evolution of the superconductivity parameters as a function of samples ageing, in order to determine the influence of “impurities” and defects on their superconducting behaviour and thus to bring eventual indications of an unconventional character
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DOUIFI, LEILA. "Detection par resonance paramagnetique electronique et par thermoluminescence d'aliments ionises." Aix-Marseille 3, 1999. http://www.theses.fr/1999AIX30041.
Full textAbstract:
L'ionisation est un procede recent qui permet d'assainir et d'augmenter la duree de conservation des aliments. Cette technique est amenee a se developper dans un proche avenir, les autorisations de mise sur le marche de produits ayant subi un traitement ionisant etant en nombre croissant. Afin de pouvoir faire respecter l'etiquetage, il est important de pouvoir mettre en evidence ce type de traitement. Pour cela il existe cinq protocoles officiellement reconnus mais aucun ne s'applique aux coquillages. Ce travail a consiste d'une part a mettre au point de nouveaux protocoles d'identification d'aliments ionises, et d'autre part a permettre la revision de ceux existant deja. Afin de supprimer des problemes d'intoxication dus a la presence de bacteries, il est fort probable qu'un pays comme les etats-unis autorise dans un proche avenir le traitement ionisant des coquillages aussi bien a l'etat frais que congele. Nous nous sommes donc interesses dans un premier temps a la detection par resonance paramagnetique electronique (rpe) et par thermoluminescence (tl) de coquillages ionises. Ces deux techniques physiques bien adaptees pour des produits solides et secs nous ont permis de mettre en evidence trois familles de coquillages irradies presentant chacune un signal different. L'utilisation de techniques telles que l'infrarouge, la diffraction par rayons x ou encore la technique de torche a plasma nous a permis d'expliquer les differences existant entre les divers echantillons temoins ou irradies. La duree du signal etant dans tous les cas detectable bien au dela du temps de stockage, nous avons pu proposer deux protocoles de detection de coquillages ionises, un par rpe et un par tl. Nous nous sommes egalement interesses a la detection d'autres produits comme les fruits, les legumes deshydrates ou encore les epices. En ce qui concerne la detection des fruits par rpe, nous avons pu etablir une classification en fonction du signal observe. Ces signaux sont de trois sortes, type cellulose, type sucre et type amidon. Notre etude a permis d'elargir le champ d'application du protocole de detection par rpe de produits riches en cellulose. Nous avons utilise la tl pour la detection de legumes et de fruits deshydrates. Ce travail a fait l'objet d'une intercomparaison entre plusieurs laboratoires europeens et a conduit a l'elargissement du domaine d'application. Apres avoir applique la methode officielle de detection par tl sur du poivre ionise, nous avons mis au point une methode alternative et propose un protocole. Cette methode alternative permet un gain de temps considerable.
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Florentín, Matthieu. "Irradiation impact on optimized 4H-SiC MOSFETs." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/395187.
Full textAbstract:
Silicon (Si) power device’ technologies have reached a high maturity level, but current
limitations on mechanic, temperature operation and electric performances require to investigate other semiconductor materials that can potentially compete with and overcome those border issues. This is the case of Silicon Carbide (SiC) and Gallium Nitride (GaN) which are becoming serious competitors to the Si due to their superior physical properties. Concerning SiC, the 4Hpolytype seems to be the best suitable candidate for high power MOSFETs according to its band gap, electric field strength, electron bulk mobility, and attainable threshold voltage, among others. But still, technological processes must be optimized in order to SiC MOSFETS can compete with their Si counterparts. This is the case of the gate oxidation process. A reduction of interface charge density is required for threshold voltage stability, and further improvements of the interface quality are also needed for high inversion mobility values. Once solved these problems, a path toward new perspectives of high power applications will be opened.
This work is the direct continuation of the Aurore Constant’s work. It is focused on 4HSiC
based devices, more specifically on the gate oxidation processes and their behaviour under
different harsh environments. Up to now, most of the works carried out were focused on the
improvement of the Silicon Dioxide-Silicon Carbide (SiO2/SiC) interface quality. Solving those
problems would allow designing high-speed and low-switching losses MOSFETs. In the past
work, the main strength was focused on a new surface pre-treatment and on a gate oxidation
process. Results showed improved electrical performances. However, we are convinced that
better values can be obtained by optimizing the post-oxidation annealing step, by performing
surface counter doping or by performing special irradiation treatments. All the efforts of this
work will oriented to the development of reliable SiC MOSFETs with improved electrical
parameters, which can operate under harsh environments (like high temperature or
proton/electron irradiated environment). Thus, the mains guidelines of this Ph. D. Thesis are in accordance with the following lines:
1. State of the art on various SiC related fields.
2. Electrical characterization processes.
3. Proton irradiation impact on 4H-SiC MOSFETs and charge build-up mechanisms theory at
the SiO2/SiC interface.
4. Electron irradiation impact on 4H-SiC MOSFETs.
5. Gate oxidation and implantation processes optimization.
6. Robustness limit of the improved processes under irradiation environments.Las tecnologías de dispositivos de potencia en silicio (Si) han alcanzado una gran madurez. Sin embargo, las limitaciones del Si debidas a sus restricciones mecánicas, térmicas y eléctricas hacen necesario otros materiales semiconductores que puedan competir con el Si y superar sus limitaciones. Este es el caso del Carburo de Silicio (SiC) y del Nitruro de Galio (GaN) que ya comienzan a ser serios competidores del Si debido a sus mejores propiedades físicas. En lo que respecta al SiC, el politipo 4H es el candidato más adecuado para la integración de MOSFETs de potencia debido, entre otros, a los valores del bandgap, campo eléctrico crítico, movilidad volumíca de los electrones y tensión umbral alcanzable. A pesar de estas ventajas teóricas del material, es necesario optimizar cada uno de los procesos tecnológicos involucrados en la fabricación de un MOSFET en SiC para que realmente pueda competir con su contrapartida en Si. Este es el caso del proceso de oxidación para la formación del dieléctrico de puerta. Concretamente, una buena estabilidad de la tensión umbral del componente requiere disminuir la densidad de cargas en la interfase óxido/semiconductor, y mejoras adicionales en la calidad de esta interfase son también necesarias para obtener altos valores de la movilidad de los portadores en el canal de inversión. La solución de los problemas tecnológicos anteriormente enunciados abrirá nuevas perspectivas a las aplicaciones de alta potencia. Este trabajo es una continuación directa del de Aurore Constant. Se centra en dispositivos basados en 4H-SiC, y más específicamente en los procesos de oxidación de puerta, y de sus comportamientos eléctricos en diferente ambientes de trabajo hostiles. Hasta la fecha, la mayor parte de la investigación se ha centrado en la mejora de la calidad de la interfase dióxido de silicio/carburo de silicio (SiO2/SiC). La solución de estos problemas debería permitir el diseño de MOSFETs muy rápidos y con pérdidas de conmutación muy bajas. El objetivo del trabajo previo de Aurore Constant fue encontrar un nuevo procedimiento de limpieza de la superficie antes de realizar la oxidación, y en definir un nuevo proceso de oxidación para la formación del dieléctrico de puerta. Los resultados obtenidos mostraron claras mejoras del comportamiento eléctrico de los componentes. Sin embargo, estamos convencidos que la mejora podría ser aún mayor optimizando la etapa del recocido post-oxidación, utilizando un proceso adicional de dopaje superficial, o realizando un adecuado proceso de irradiación. Todos los esfuerzos de este trabajo se han dirigido al desarrollo de MOSFETs en SiC fiables, con mejores características eléctricas, y capaces de trabajar en ambientes de alta temperatura y de irradiación protónica o electrónica. En resumen, las principales líneas de esta Tesis son las siguientes: 1. Estado del arte de los diferentes dominios de trabajo del SiC. 2. Procesos y técnicas de caracterización eléctrica. 3. Impacto de la irradiación de protones en MOSFETs fabricados en 4H-SiC, y descripción teórica de los mecanismos de creación de carga en la interfase SiO2/SiC. 4. Impacto de la irradiación electrónica en MOSFETs fabricados en 4H-SiC. 5. Optimización de los procesos de oxidación y de implantación. 6. Límite de robustez de los procesos tecnológicos optimizados en ámbitos irradiados.
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Hayward, Erin M. G. "Atomistic studies on irradiation damage in iron." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34004.
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Two topics involving irradiation damage in alpha-iron have been considered. First, damage cascades representative of those that would be induced by radiation have been simulated using molecular dynamics (MD). The number and type of defects produced are compared for pure iron and iron with a small hydrogen concentration. Second, the inter- action energy between point defects and line dislocations has been calculated for a number of configurations, using both molecular statics methods and calculations based on linear elastic continuum theory and the dipole force tensor. Results from both methods are com- pared. Results from these two topics are relevant for predicting macroscopic behaviors such as creep and plasticity in reactor structural materials.
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Canitez, Nazife. "Pasteurization of Apple Cider with UV Irradiation." Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/CanitezN2002.pdf.
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Tabtiang, Arunee. "Irradiation crosslinking of oriented plasticised PVC compounds." Thesis, Loughborough University, 1995. https://dspace.lboro.ac.uk/2134/12433.
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Plasticised polyvinyl chloride (PPVC) compounds were biaxially stretched, annealed in the drawn state and subsequently exposed to electron beam irradiation. During sample irradiation the crosslinking reaction was promoted by a radiation sensitising monomer, trimethylolpropanetrimethacrylate (TMPTMA), included in the PVC compound formulations. The influence of stabiliser type and level, TMPTMA level and irradiation dose on the network structure produced was investigated. A tin stabiliser, Stanclere TL, was selected for this study as it promoted the crosslinking reaction and it showed no interfering peaks in the wide angle x-ray diffraction (WAXD) traces which were used to follow the development of structural order. The appearance of gel, the material insoluble in THF, in irradiated oriented samples proved that a crosslinked structure was created. The gel formation increased with TMPTMA level and irradiation dose. The gel content was found to affect mechanical properties at elevated temperatures and produced an increase in the area shrinkage temperature. Sample thickness and the plasticiser content were found to have a major effect upon gel formation. The thicker the sample was, the smaller the quantity of gel that was formed. Samples containing 46.5phr plasticiser showed greater gel content than samples containing 25phr plasticiser as a result of the higher molecular mobility in the more plasticised samples. It was also found that the orientation of the film decreased the efficiency of network formation in PVC formulations with a 46.5phr plasticiser content but no significant change in gel content could be detected in those containing 25phr plasticiser. Tensile properties and impact strength at room temperature were slightly improved in irradiated samples. The modified structure resulted in an improvement in tensile strength and penetration resistance at higher temperatures and an increased area shrinkage temperature. Crosslinking did not affect room temperature recovery or crystalline orientation; however irradiation crosslinking reduced crystallinity.
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Franzén, Lars. "Effects of fractionated irradiation on salivary glands." Doctoral thesis, Umeå universitet, Onkologi, 1992. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-101770.
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The thesis is a study of the effects of radiation on the salivary glands in an experimental and a clinical study. Irradiation is a cornerstone in the management of head and neck cancer and is as other modalities of cancer treatment, afflicted with adverse reactions. An optimal radiotherapy regime is limited by the sensitivity of the normal tissues with regard to early and late effects. In certain cases the early effects can be so troublesome that it will cause interruption in the irradiation and questioning of the curative intention. Although DNA is the lethal target, other parts of the cell have been proposed as sensitive targets to irradiation. Different in vitro secretory models and quantitative morphological characterization and immunohistochemical evaluation of neuropeptides were performed in rat salivary glands after irradiation. The irradiation was given unilaterally or bilaterally once a day for a five-day schedule with 6 MV photons (total dose 20, 30, 35, 40, 45 Gy) or a two fractions regime in five days with a total dose of 24 or 32 Gy. The contralateral gland served as a control for unilaterally treated animals and parallel analyses were done 10 days or 180 days following the last irradiation dose. An early, dose-dependent effect of fractionated irradiation on noradrenaline-stimulated potassium fluxes (86Rb+ fluxes) was demonstrated. In contrast, the exocytotic amylase release displayed no obvious alterations, and morphologically no changes were seen. Regarding late effects (180 days) the noradrenaline-stimulated electrolyte secretion was decreased at least for the higher doses of irradiation. Amylase content and loss of acini was also dose-dependently decreased. At 10 days after bilateral irradiation there was a marked increase in the expression of the neuropeptides substance P, leu-enkephalin and bombesin in the ganglionic cells associated with the submandibular glands and in nerve fibers of the glandular parenchyme. In addition, a clinical prospective evaluation of 25 patients was performed before, during radiotherapy and 6, 12 and 18 months after the end of treatment. A great interindividual variation in the recovery was demonstrated with regard to salivary flow rate. Irradiation doses about 40-50 Gy caused generally reversible changes; sometimes salivary secretion was almost completely restored 6-18 months after the end of radiotherapy. Doses exceeding 65 Gy induced almost irreversible alterations. Even if DNA is the target for the lethal effect of irradiation, other constituents, such as the cell membrane or neuropeptide expression can be significantly affected by irradiation and cause important physiological changes.S. 1-43: sammanfattning, s. 47-164: 6 uppsatser
digitalisering@umu
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El-Shaweesh, Kamal Husein. "Tissue culture and irradiation studies in Solanum." Thesis, University of Salford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334320.
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Amjad, Muhammad. "Seed irradiation in relation to moisture content." Thesis, University of Salford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281596.
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Murphy, Susan Mary. "Theory of compositional effects in irradiation damage." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670365.
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London, Andrew James. "Irradiation damage of oxide dispersion strengthened steels." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:4860651a-e919-449c-9e1c-8c6843adddd2.
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Advanced fission and fusion power offer long-term energy production from fundamentally carbon-free fuel sources, with high-energy densities and high reliability. However, for these power sources to be realised, many materials challenges need to be addressed. Oxide dispersion strengthened (ODS) ferritic alloys are recognized as potential fission fuel cladding and fusion structural materials because of their high-temperature stability and swelling-resistance imparted by the nano-scale oxide clusters they contain. This work presents the study of a set of model ODS alloys with a systematic variation in alloy chemistry in order to investigate the influence of chemical additions on the oxide cluster nature and the irradiation resistance. To investigate these properties, the high-resolution characterisation techniques of atom probe tomography and transmission electron microscopy were applied in combination with nanoindentation to assess mechanical properties and X-ray diffraction to study the crystallinity. The quantification of the character of the oxide particles in these ODS alloys by atom probe tomography presented a number of challenges and I extend the conventional analysis techniques in order to overcome these difficulties. By comparison of the addition of Ti, and then Cr, to a Fe-Y2O3 alloy, the influence of alloy chemistry on the oxide particles was evaluated. The main aims were to investigate the microstructure, the oxide cluster composition and to set a baseline to which the irradiated samples were compared. The irradiation damage of the oxide clusters was investigated using ion irradiation as an analogue for neutron damage. Irradiation experiments were performed at a range of temperatures and the stability of the clusters was assessed based on their size, number density and chemistry. Subtle changes in cluster chemistry at elevated temperatures and the dramatic changes which occurred after irradiation at low temperatures lead to conclusions about the competition of thermal diffusion and irradiation damage.
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Hang, Shuojin. "Irradiation-based defect engineering of graphene devices." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/388184/.
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The addition of structural defects modifies the intrinsic properties of graphene–the two dimensional allotrope of carbon. The controlled introduction of such defects is therefore desired to realise specific functions. For instance, the grain boundaries formed between epitaxial grown graphene domains has been observed to mimic a metallic wire. By contrast, the presence of point defects in a graphene channel affects the carrier transport significantly in a manner such as the Fermi-level pinning, transport-gap widening and Anderson localization. Incorporating these defects into conventional device structures can open up a new horizon for device engineering. In this work, I propose and explore the defect engineering of graphene devices via ion bombardment using a helium ion microscope (HIM). The lithographic advantage of HIM is demonstrated for various graphene nanostructures such as fully gated 20nm double quantum dots and 10nm nanoribbons, upon which a hybrid EBL-HIM fabrication technique is developed for device integration. Graphene irradiated with HIM up to 5×1014 cm-2 shows a transition from Stage 1 to Stage 2 disorder as probed by confocal Raman spectroscopy. For the first time, the damage of ion-beam-milling on a graphene-onsubstrate sample is visualised. The spatially resolved Raman map shows that the beam damage can extend to a few hundred nm around the 30nm cut, which is attributed to the damage due to backscattered helium ions and recoils from the substrate. Furthermore, the electrical properties of irradiated graphene nanoribbons (iGNR) is characterised. As irradiation dose increases, the iGNR devices shows an abrupt decrease in mobility and interestingly an asymmetric decrease of conductance in the electron and hole conduction branches. This is then related to the pinning of Fermi level in iGNR, a unique property caused by irradiation. This is believed to be associated with additional dangling bonds (scattering centres) created by irradiation, as supported by XPS analysis. Based on these properties, a new graphene device structure is explored, in which irradiated regions are used as energy barriers. The temperature-dependent conductance shows the signature of thermal-activated variable range hopping (VRH) at intermediate temperature. The localisation lengths extracted from hopping temperature showed good agreement with that from length-dependent conductance. Furthermore, the activationless VRH is observed for relatively high electric field.
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SMAALI, MOHAMMED. "Heterodiffusion et irradiation gamma du quartz alpha." Besançon, 1998. http://www.theses.fr/1998BESA2051.
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L'objet de ce travail etait l'etude par spectrometrie du comportement des defauts dans le quartz, soumis a deux traitements : - le premier consiste a eliminer, sous l'effet d'un champ electrique et a temperature elevee, les impuretes interstitielles presentes dans le cristal : c'est le balayage ou sweeping out. - le second consiste a introduire, dans le cristal un heteroatome sous l'effet d'un champ electrique et a temperature elevee. Nous avons applique ceci, soit a des quartz non traites, soit aux quartz sweepes sous air ou sous atmosphere d'azote en utilisant differents cations alcalins comme heteroatome : c'est le dopage ou sweeping in. Les effets des irradiations se sont montres plus importants dans le cas des quartz non traites (synthetiques ou naturels), et les quartz naturels dopes. Le recuit des quartz de synthese non traites permet la restauration d'une partie des defauts initiaux. Le recuit n'a pas modifie les spectres ir des quartz de synthese traites. Le recuit des quartz naturels, traites ou non, permet a une certaine partie des defauts de retrouver leur etat initial. Lors de l'operation de recuit, nous avons enregistre les courbes de thermoluminescence. Les traitements tels que le sweeping, le dopage et l'irradiation, appliques a differents types de cristaux, nous ont permis de distinguer plusieurs maxima et de les attribuer a un ou plusieurs types de defauts. L'etude des quartz colores par spectroscopie infrarouge permet de determiner leur mode de cristallisation, naturelle ou de synthese. Nous avons montre que chaque espece coloree, possede ses propres criteres pour l'identification de son origine.
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Ding, Jing-Jie. "Irradiation of water ice and astrophysical implication." Caen, 2014. http://www.theses.fr/2014CAEN2056.
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Les glaces sont présentes dans notre système solaire par exemple sur les comètes, les lunes de Jupiter et de Saturne ainsi que sur les objets trans-neptuniens. Dans le milieu interstellaire, ces glaces forment une fine couche à la surface de grains des nuages denses. L’eau (H2O) est la molécule la plus abondante dans ces glaces. Ces glaces sont constamment exposées aux rayons cosmiques, au vent solaire et aux ions piégés dans la magnétosphère des planètes géantes. Les simulations de ce type d’irradiation associées aux observations peuvent nous amener à comprendre la grande variété des processus physicochimiques induits par l’irradiation. Nous avons donc irradié des glaces avec les ions produits par le GANIL afin de simuler les effets des rayons cosmiques pour les ions lourds rapides et les effets du vent solaire pour les ions lents. Les modifications induites sont étudiées par spectroscopie infrarouge dans le domaine 500-5000 cm-1. L’irradiation induite des changements de structure tels que la compaction et l’amorphisation. Plusieurs ions ont été utilisés afin de déterminer la dépendance de ces processus physiques en fonction du pouvoir d’arrêt du projectile. A basse énergie l’implantation d’ions soufre a permis de mesurer le taux de production de l’acide sulfurique H2SO4, molécule observée à la surface d’Europa. La comparaison avec les observations et les mesures de flux des ions soufre à la surface d’Europa amène à penser que le processus d’implantation est primordial pour expliquer la présence de H2SO4 sur cette lune de Jupiter. Finalement, une étude préliminaire sur le rôle de l’interface entre un substrat carboné et une glace de NH3+H2O est présentéeIces can exist in our solar system for example on comets, the moons of Jupiter and Saturn, and trans-Neptunian objects. In the cold interstellar medium, they form thin layers on dust grains. Water (H2O) is the most abundant molecules in those ices, which are continuously exposed to the irradiation by cosmic rays, solar wind, and ions trapped in the magnetosphere of the giant planets. Simulation in the laboratory compared to telescopic observations can provide information to understand the large variety of radiation induced physicochemical processes. Therefore, we simulated the effects of swift heavy ion (cosmic ray analogs) and slow ion (solar wind, magnetosphere ions) irradiation of water ice at different beam lines of the GANIL accelerator facility. Fourier transform infrared spectroscopy (FTIR) was used to analyze the ices. The irradiation induced structural changes of water ice such as amorphization and compaction were studied. The efficiency to amorphize and compact the ice was established as a function of projectile stopping power with several swift heavy ions. Furthermore, by implantation of sulfur ions in water ice, the formation yield of sulfuric acid was measured and found to increase with projectile energy. From comparison to measure sulfur ion fluxes and sulfuric acid concentrations by the Galileo spacecraft, strong evidence was found that H2SO4 on Europa’s surface can be formed by sulfur ion implantation of magnetosphere ions in water ice. Finally, we also performed a first preliminary experiment to study the radiation induced chemistry with a carbonaceous solid substrate covered with a NH3+H2O ice mantle
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Devary, Yoram. "Response of mammalian cells to ultraviolet irradiation /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9724890.
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Auvray, Marie-Hélène. "Endommagement sous irradiation de l'aluminate de lithium." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376024855.
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Yu, Cunjing. "Modulation of immune responses by UV irradiation." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/22813.
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Atopic dermatitis (AD) is a common, chronic relapsing inflammatory skin disease associated with cutaneous hyper-reactivity to environmental triggers that are innocuous to normal nonatopic individuals. AD affects 10% to 15% of children and 2% to 10% of adults in industrialized countries. There has been increasing interest in this disease triggered by its increasing prevalence in western societies and its contribution to the increasing health care costs. Yet, the underlying pathophysiologic and genetic mechanisms leading to the manifestation of AD are not clear. AD results from a complex interplay between environmental triggers, susceptibility genes including mutations in the keratinocyte protein filaggrin and altered immune responses resulting in allergic CD4+ T cell (Th2) immunity to epidermally encountered antigens. Regulatory T cells (Tregs) play an important role in controlling responsiveness to self-antigens and preventing autoimmune diseases, as well as in limiting inflammatory responses during inflammation and infection. Currently, studies investigating the number and function of Tregs in patients with AD have shown controversial results. It has been long established that symptoms of AD improve on exposure to sunlight. Narrowband UVB (NB-UVB) phototherapy is a common treatment modality for a variety of skin diseases. Considering the adverse effects for systemic treatment for severe adult AD, phototherapy, especially NB-UVB phototherapy may be a more practical long-term treatment. However, approximately 50% of patients over an 8-week treatment course do not improve after NB-UVB phototherapy. Therefore, it is important to identify characteristics of AD patients to determine whether they will respond to phototherapy and to avoid adverse effects for unresponsive patients. UVB exposure has also been associated with induction of Tregs in mice and increasing their numbers and/or functional capacity may offer benefit to patients with chronic AD. Active vitamin D (1,25(OH)2D3), one of the factors induced by UV-B radiation induces Tregs and is suggested to contribute to the suppressive effect of NB-UVB phototherapy. However, UV radiation could also have beneficial effects through other pathways known to affect immunoregulation. UVB exposure upregulates production of nitric oxide (NO) in the skin which also affects immune cell function. The protein filaggrin is broken down in differentiating keratinocytes to form the natural moisturizer of the skin. The gene encoding filaggrin (FLG) has been shown to be a major predisposing factor for AD. A key breakdown product is urocanic acid (UCA) which also acts as a natural sunscreen and undergoes trans-cis isomerisation on exposure to UV-B. Cis-UCA is known to modulate immune responses, however, the mechanisms of its action remain elusive. The production of all three compounds, vitamin D, cis-UCA and NO might all increase in the circulation of patients undergoing UVB phototherapy. While the immunomodulatory effect of Vitamin D is well described, cis-UCA and NO may also affect the behaviour of T lymphocytes systemically. Therefore, I investigated the effect of NO and cis-UCA on the phenotype and function of CD4+T cells and monocyte-derived dendritic cells (Mo-DCs) derived from peripheral blood mononuclear cells (PBMCs) from healthy volunteers. I also investigated the correlation between plasma concentration of 25(OH) vitamin D and nitrate, FLG genotype, circulating Tregs and clinical efficacy of NB-UVB phototherapy. My results showed that NO did not affect the phenotype of human mo-DCs and directly affected peripheral CD4+ T cells by inducing functional CD25+Foxp3+CD127-Tregs from CD4+CD25lo/- effector T cells. Moreover, NO increased expression of the of skin homing marker CLA on these Tregs, suggesting an increased ability of NO-induced Tregs to migrate to the skin. These NO-induced CD25+Foxp3+CD127-Tregs had immunosuppressive functions and inhibited autologous CD4+ T cell proliferation. Cytokines, at least IL-10, secreted by NO-treated CD4+ T cells were not sufficient for the suppressive function of NOinduced Foxp3+Tregs. The immune regulatory function of NO-induced Fopx3+Tregs required cell-cell contact and was mediated by membrane bound TGFβ and PD-1/PD-L1 but not CTLA-4. Results also showed that cis-UCA might have both pro- and anti-inflammatory effects. Cis- UCA significantly decreased the proportion of CD25hi Foxp3+ cells from activated CD4+ T cells. It also decreased the expression of vitamin D receptor in CD4+ T cells which may interfere with the immune regulatory function of vitamin D. These results suggested that there might be a fine balance between UV-induced anti-inflammatory molecules’ effect on CD4+ T cells. However, Cis-UCA also modulated CD4+ T cell directly by decreasing CD4+ T cell proliferation, decreasing phosphorylation of ERK after TCR activation, enhancing immune suppressive cytokines secretion, and inhibiting the percentage of CLA+CD4+T cells suggesting a decreased ability to migrate to the skin, . Cis-UCA also affected the phenotype and function of antigen presenting cells by decreasing the expression of HLA-DR, CD86 and CD40 on immature mo-DCs, which led to increased proportion of CD25+Foxp3+CD127- T cells when co-cultured with allogenic CD4+ T cells. Results generated from the clinical study in which all 29 patients got better after phototherapy suggested although circulating 25 (OH) vitamin D concentration was significantly increased after NB-UVB phototherapy, the change of circulating 25 (OH) vitamin D concentration did not correlate with disease improvement. This suggests that vitamin D is not the only pathway involved and that other molecules contribute to UVB-induced immune-regulation. The data also show that of the levels of circulating nitrate and the FLG genotype did not correlate with improvement / change with phototherapy. However, the expression of CD69 and CLA on circulating CD4+ T cells was decreased after treatment suggesting that UVB affected T cell activation and migration to the skin, and their importance in determining clinical responses requires further investigation. Taken together, the results from my study provide evidence that vitamin D is not the only molecule responsible for the beneficial effect of NB-UVB phototherapy. NO and cis-UCA may down-regulate immune responses by affecting human peripheral CD4+ T cells and mo- DCs phenotype and function. A further understanding of the effect of NO and cis-UCA on skin resident immune cells will provide more insights for narrowing NB-UVB phototherapy which will help to select patients that most likely to benefit from a mechanism-based treatment.
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Gee, Hannah. "Effects of space irradiation on astronaut bodies." Thesis, Boston University, 2013. https://hdl.handle.net/2144/21154.
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Thesis (M.A.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.The effects of space irradiation on the cardiovascular systems remain a great mystery. After conducting studies on survivors of the atomic bomb, radiotherapy as a treatment for cancer and other diseases, and health data of astronauts who have participated in short and long duration space missions, the overall conclusion is that ionizing irradiation of any type results in cardiovascular damage. Problems manifest decades after irradiation exposure and the accumulating health complications have led to fatalities. However, little is known about space irradiation and how it affects our bodies. Predictive models that were developed to date were created based on events that have occurred on earth. National Aeronautics and Space Administration (NASA) plans for manned missions to the Moon and Mars in the near future. There is a great need for ground-based studies about the effects of cosmic irradiation on the human body. We examined molecular pathways in the heart tissue of adult 7-9 months old mice, an equivalent of middle-age for astronauts (35-55), after receiving a single low dose full body of either 56Fe (iron) or 1H (proton) irradiation + aging of 1, 3, and 10 months. We also investigated mice after 56Fe or 1H irradiation + aging of 1, 3, and 10 months, and 3 days after an induced acute myocardial infarct (AMI). Western blot analyses were performed for proteins involved in cardiac function and cardiac recovery. Results indicated that 56Fe irradiation impaired cardiac function significantly during aging and continued to worsen with age. AMI results were less straightforward. The younger, 56Fe irradiated mice revealed a significant decrease in the expression of proteins associated with survival of cardiac tissue. The older, 1H irradiated mice group revealed a significantly decreased expression of proteins associated with survival of cardiac tissue. The 10 month 56Fe irradiated mice did not show compensatory mechanisms and the cardiac protein expression levels were attributed to aging. While the 10 month 1H irradiated mice compensated and required less repair activation.
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Pallikarakis, Christos. "Ion irradiation effects on Si nanocrystal properties." Thesis, KTH, Tillämpad fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-256346.
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