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Perks, Jonathan Michael. "Phosphorus segregation and diffusion in nickel and Fe-Cr-Ni alloys under fast particle irradiation." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329993.
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Terentyev, Dmitry. "Study of radiation effects in FeCr alloys for fusion applications using computer simulations." Doctoral thesis, Universite Libre de Bruxelles, 2006. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210787.
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Galloway, Graham. "Computational study of radiation damage and impurity effects in iron based alloys." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9908.
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Molecular dynamics techniques are used to explore metals at an atomic level. The focus of the studies is the effects of irradiation on a metallic system. Ion surface bombardment effects, bulk cascades and interaction with voids and bubbles in bulk are studied. In the first section a study of a copper <110> surface being bombarded by low energy argon ions is conducted. Molecular dynamics simulations were used to study the surface impact crater formation and the damage caused in the surrounding area. Another group had previously performed experimental measurements on the same system. The simulation data is compared to experiment, in order to validate the molecular dynamics technique. Additionally, information about the formation of the craters at time scales inaccessible to experiment can be gained. In the next section bulk radiation induced cascades in BCC iron are considered. Cascades of energy 1 keV, 2 keV, and 5 keV are initiated in the bulk of the material and the damage yields studied. Cascades are also studied in proximity to voids and helium bubbles in the bulk. The damage formation processes and damage yields in these cascades is analysed. A mechanism that allowed voids to be ballistically moved by the cascade was observed. To further explore this an object kinetic Monte Carlo model was written to simulate the effects of this motion on the diffusion of the voids. The final section is a study of transition metals as alloying elements in BCC iron. This system is of interest as it would be a model for various steels used in construction and shielding. A set of potentials describing iron with low concentrations of transition metals has previously been developed by a different group. These potentials were implemented in the molecular dynamics code. The equilibrium properties of various alloys are explored by implementing a Metropolis algorithm to minimise the Gibbs free energy of the system. Various binary and tertiary alloys are analysed and compared with experimental values in the literature. The attraction of the elements to voids present in the system is also studied.
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Huang, Liangzhao. "Multiscale modeling of the radiation-induced segregation in Ni-based and Fe-based dilute alloys." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP048.
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Nous présentons une modélisation quantitative de la redistribution des défauts ponctuels (DPs) et de la ségrégation induite par irradiation (SII) sur les défauts étendus, dans des alliages modèles dilués Ni(B ≡ Ti, Cr) et Fe(B ≡ P, Mn, Cr, Si, Ni, Cu). Le changement de composition chimique au voisinage des défauts étendus joue un rôle décisif sur l’évolution de la microstructure et les propriétés mécaniques d’un matériau. L’irradiation génère des défauts ponctuels, qui diffusent en s’échangeant avec les atomes voisins, s’annihilent en se recombinant entre eux ou en interagissant avec des défauts étendus (qui agissent comme des puits de DPs). Les flux de DPs vers les puits induisent des flux atomiques dans le même sens ou le sens opposé des flux de DPs, produisant ainsi la SII aux puits. Nous étendons la théorie de champ moyen auto-cohérent aux déplacements atomiques forcés (DAF), mécanismes de diffusion athermiques générés par une cascade de déplacements sous irradiation. L’implémentation de nos développements théoriques dans le code KineCluE, nous permet de calculer les flux de DPs et d’atomes, et leurs couplages. A partir du calcul des flux en fonction de la température, de la composition, et du champ de déformation ; et d’un traitement de type cinétique chimique des réactions de production et d’annihilation des DPs, nous obtenons les profils stationnaires de SII. Dans chacun des régimes cinétiques particuliers pour lequel, l’une des réactions des DPs domine par rapport aux autres, nous obtenons les expressions analytiques des profils stationnaires des DPs et solutés sur les puits planaires. Pour rendre compte de l’effet du champ de déformation généré par une dislocation coin sur la SII et sur les taux d’élimination des DPs sur la dislocation, nous résolvons numériquement les équations d’élastodiffusion. A partir d’une base de données ab initio des énergies de liaison, des dipôles élastiques, et des fréquences d’échange atome-DP dans, nous réalisons une étude systématique des effets de la microstructure et des conditions d’irradiation sur les propriétés de diffusion, les taux d’élimination des DPs aux puits, et la SII. Nous montrons que : (i) les boucles de dislocations sont enrichies en Ni dans Fe(Ni) et appauvries en Ti dans Ni(Ti), et les quantités ségrégées sont en bon accord avec les valeurs expérimentales mesurées dans les alliages modèles Fe(Ni) et Ni(Ti) irradiés aux ions ; (ii) à fort flux, basse température, et grande force de puits de la microstructure, les évènements DAF réduisent sensiblement la SII, tout particulièrement dans les alliages base Ni ; (iii) les décalages en température calculés pour simuler les effets d’une irradiation aux neutrons par une irradiation aux ions, peuvent être très différents selon le phénomène induit par irradiation que l’on étudie, le régime cinétique dans lequel le système évolue, et la nature chimique de l’alliage étudié ; (iv) l’interaction entre les DPs et les atomes de soluté modifie le facteur de biais d’absorption entre lacunes et interstitiels d’une dislocation coin. Ainsi l’ajout de Ni produit un biais négatif alors que l’ajout de Mn augmente le facteur de biais (jusqu’à 200% de la valeur dans Fe pur sous contrainte), suivant la température et la composition ; (v) la contrainte augmente significativement la quantité de la ségrégation de soluté dans Fe(Ni) (par exemple, 400% de la valeur sans élasticité à 400K), et change le signe de la SII dans Fe(Cr)We present a quantitative modeling of the point-defect (PD) redistribution and solute radiation-induced segregation (RIS) at extended defects in dilute Ni(B ≡ Ti, Cr) and Fe(B ≡ P, Mn, Cr, Si, Ni, Cu) alloys. The change in chemical composition, in the vicinity of extended defects, plays a decisive role on the evolution of the microstructure and mechanical properties of materials. Irradiation produces PDs, that diffuse by exchanging with neighboring atoms, annihilate by mutual recombination or by interacting with extended defects (that act as PD sinks). The fluxes of PDs towards sinks lead to atomic fluxes in the same or opposite direction of the PD flux; thereby producing RIS at sinks. We extend the self-consistent mean-field theory to forced atomic relocations (FARs), athermal diffusion mechanisms generated by displacement cascades under irradiation. The implementation of the extended theory in the KineCluE code allows us to compute PD and atomic fluxes, and their couplings. From the calculation of fluxes as a function of temperature, composition, and strain field; and a mean-field treatment of the production and annihilation reactions of PDs, we obtain the steady-state RIS profiles. In each of the particular kinetic regimes for which one of the PD reactions dominates over the others, we derive analytical expressions of steady-state profiles of PDs and solute atoms at planar sinks. To account for the effect of strain generated by an edge dislocation on the RIS and PD elimination rates, we numerically solve the elastodiffusion equations. Based on an ab initio database of binding energies, elastic dipoles, and atom-PD exchange frequencies, we perform a systematic study of the effects of the microstructure and irradiation conditions on diffusion properties, PD elimination rates at sinks, and RIS. We show that: (i) the dislocation loops are enriched in Ni in Fe(Ni) and depleted in Ti in Ni(Ti), and the calculated amounts of RIS are in good agreement with the experimental values measured in model Fe(Ni) and Ni(Ti) alloys irradiated by ions; (ii) at high flux, low temperature, and high sink strength, forced atomic relocations significantly reduce RIS, especially in Ni-based alloys; (iii) the temperature shifts calculated to simulate the effects of neutron irradiation by ion irradiation can be very different depending on the radiation-induced phenomenon, the kinetic regime in which the system evolves, and the chemical nature of the investigated alloy; (iv) the interactions between PDs and solute atoms change the absorption bias between vacancies and interstitials of an edge dislocation, as for instance, the addition of Ni leads to a negative bias while the addition of Mn increases the bias factor (up to 200% of the strained pure Fe value), depending on temperature and composition; (v) the dislocation strain field significantly increases Ni RIS (e.g., about 400% of the strain-free value at 400K) in Fe(Ni), and changes the sign of RIS in Fe(Cr)
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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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Umana-Membreno, Gilberto A. "A study of gamma-radiation-induced effects in gallium nitride based devices." University of Western Australia. School of Electrical, Electronic and Computer Engineering, 2006. http://theses.library.uwa.edu.au/adt-WU2007.0015.
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[Truncated abstract] Over the past decade, the group III-nitride semiconducting compounds (GaN, AlN, InN, and their alloys) have attracted tremendous research efforts due to their unique electronic and optical properties. Their low thermal carrier generation rates and large breakdown fields make them attractive for the development of robust electronic devices capable of reliable operation in extreme conditions, i.e. at high power/voltage levels, high temperatures and in radiation environments. For device applications in radiation environments, such as space electronics, GaN-based devices are expected to manifest superior radiation hardness and reliability without the need for cumber- some and expensive cooling systems and/or radiation shielding. The principle aim of this Thesis is to ascertain the level of susceptibility of current GaN-based elec- tron devices to radiation-induced degradation, by undertaking a detailed study of 60Co gamma-irradiation-induced defects and defect-related effects on the electrical characteristics of n-type GaN-based materials and devices . . . While the irradiation-induced effects on device threshold voltage could be regarded as relatively benign (taking into account that the irradiation levels employed in this study are equivalent to more than 60 years exposure at the average ionising dose rate levels present in space missions), the observed device instabilities and the degradation of gate current characteristics are deleterious effects which will have a significant impact on the performance of AlGaN/GaN HEMTs operating in radiation environments at low temperatures, a combination of conditions which are found in spaceborne electronic systems.
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Piochaud, Jean-Baptiste. "Modelling of radiation induced segregation in austenitic Fe alloys at the atomistic level." Thesis, Lille 1, 2013. http://www.theses.fr/2013LIL10024/document.
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Dans les réacteurs à eaux pressurisée, les internes de cuve sont soumis à d’intenses irradiations induisant le mécanisme de corrosion sous contrainte assistée par l’irradiation initié par le phénomène de ségrégation induite par l’irradiation (SIR). La SIR observée dans les aciers austénitiques 316 est modélisée à l’échelle atomique en considérant un alliage ternaire modèle Fe–10Ni–20Cr. Pour atteindre cet objectif, nous avons construit un modèle d’interactions de paires pour le système Fe-Ni-Cr afin de modéliser la SIR par méthodes Monte Carlo. Le modèle d’interactions de paires fut déduit à la fois des calculs DFT (Density Functional Theory) disponibles dans les systèmes pures cubiques faces centrées, mais aussi en effectuant des calculs DFT dans l’alliage Fe–10Ni–20Cr. Les énergies de formation calculées dans cet alliage modèle dépendent fortement de l’environnement local des défauts ponctuels. Nous avons pu ainsi établir une relation liant ces énergies au nombre et à la position des atomes de Ni et de Cr se trouvant à proximité des défauts ponctuels. Dans cette étude, nous montrons qu’un modèle d’interactions de paires uniquement basé sur les interactions entre éléments positionnés sur les sites du réseau (éléments d’alliage et lacune) est incapable de prendre en compte seul à la fois les aspects thermodynamiques et cinétiques de la SIR. Une estimation plus précise des barrières de migration est requise pour les espèces migrantes que celle proposée qui ne prend pas en compte l’environnement du point col. Ce travail montre ainsi qu’il est nécessaire de réaliser des calculs DFT des énergies de migration afin d’être en mesure de calibrer un modèle utilisable dans le cadre de simulations de Monte Carlo cinétique atomique. Nous montrons également que l’ajustement de notre modèle sur les données DFT obtenues pour les interstitiels est incompatible avec la modélisation de la SIR aux électronsIn pressurized water reactors, under irradiation internal structures are subject of irradiation assisted stress corrosion cracking which is influenced by radiation induced segregation (RIS). In this work RIS of 316 stainless steels is modelled considering a model ternary Fe–10Ni–20Cr alloy. For this purpose we have built an Fe-Ni-Cr pair interaction model to simulate RIS at the atomistic level using an atomistic kinetic Monte Carlo approach. The pair interactions have been deduced from density functional theory (DFT) data available in the pure fcc systems but also from DFT calculations we have performed in the Fe–10Ni–20Cr target alloy. Point defect formation energies were calculated and found to depend strongly on the local environment of the defect. As a consequence, a rather good estimation of these energies can be obtained from the knowledge of the number and respective positions of the Ni and Cr atoms in the vicinity of the defect. This work shows that a model based only on interaction parameters between elements positioned in perfect lattice sites (solute atoms and vacancy) cannot capture alone both the thermodynamic and the kinetic aspect of RIS. A more accurate of estimating the barriers encountered by the diffusing species is required than the one used in our model, which has to depend on the saddle point environment. This study therefore shows thus the need to estimate point defect migration energies using the DFT approach to calibrate a model that can be used in the framework of atomic kinetic Monte Carlo simulations. We also found that the reproduction by our pair interaction model of DFT data for the self-interstitial atoms was found to be incompatible with the modelling of RIS under electron irradiation
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Diestelhorst, Ryan M. "Silicon-germanium BiCMOS device and circuit design for extreme environment applications." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28180.
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Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.Committee Chair: Cressler, John; Committee Member: Papapolymerou, John; Committee Member: Ralph, Stephen.
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Choi, Hong Kyu. "Analysis and modeling of the long-term performance of amorphous photovoltaic arrays." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184835.
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A validated predictive model of a-Si:H solar cell arrays was developed. The performance of a-Si:H solar cells was modeled by predicting the performance before degradation first, and then modifying it with terms that account for degradation and recovery effects. A unique approach for the determination of the fundamental rate controlling parameters for the degradation and recovery process was carried out by observing the variation of the short-circuit current. The experimental annealing of a-Si:H silicon samples showed that the percent recovery from the degraded state to the as-grown state by annealing was virtually independent of the initial state at the start of the annealing process. This allowed the recovery parameters to be determined independently of the prior degradation process. An extremely simple and fast running algorithm for the long-term performance was developed in terms of the incident solar radiation, the panel temperature, and the total radiation exposed. Also it was found that the entire process of the Staebler-Wronski effect could be adequately represented by a correlation in which the degradation and recovery processes are solely a function of the total radiation exposure of the panel at ambient conditions.
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Lourenco, Nelson Estacio. "An assessment of silicon-germanium BiCMOS technologies for extreme environment applications." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45959.
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This thesis evaluates the suitability of silicon-germanium technology for electronic systems intended for extreme environments, such as ambient temperatures outside of military specification (-55 degC to 125 degC) range and intense exposures to ionizing radiation. Silicon-germanium devices and circuits were characterized at cryogenic and high-temperatures (up to 300 degC) and exposed to ionizing radiation, providing empirical evidence that silicon-germanium is an excellent platform for terrestrial and space-based electronic applications.
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Wilcox, Edward. "Silicon-germanium devices and circuits for cryogenic and high-radiation space environments." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33850.
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This work represents several years' research into the field of radiation hardening by design. The unique characteristics of a SiGe HBT, described in Chapter 1, make it ideally suitable for use in extreme environment applications.
Chapter 2 describes the total ionizing dose effects experienced by a SiGe HBT, particularly those experienced on an Earth-orbital or lunar-surface mission. In addition, the effects of total dose are evaluated on passive devices.
As opposed to the TID-hardness of SiGe transistors, a clear vulnerability to single-event effects does exist. This field is divided into three chapters. First, the very nature of single-event transients present in SiGe HBTs is explored in Chapter 3 using a heavy-ion microbeam with both bulk and SOI platforms [31]. Then, in Chapter 4, a new device-level SEU-hardening technique is presented along with circuit-design techniques necessarily for its implementation. In Chapter 5, the circuit-level radiation-hardening techniques necessarily to mitigate the effects shown in Chapter 3 are developed and tested [32].
Finally, in Chapter 6, the performance of the SiGe HBT in a cryogenic testing environment is characterized to understand how the widely-varying temperatures of outer space may affect device performance.
Ultimately, the built-in performance, TID-tolerance, and now-developing SEU-hardness of the SiGe HBT make a compelling case for extreme environment electronics. The low-cost, high-yield, and maturity of Si manufacturing combine with modern bandgap engineering and modern CMOS to produce a high-quality, high-performance BiCMOS platform suitable for space-borne systems.
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Najafizadeh, Laleh. "Design of analog circuits for extreme environment applications." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31796.
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Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010.Committee Chair: Cressler, John; Committee Member: Papapolymerou, John; Committee Member: Shen, Shyh-Chiang; Committee Member: Steffes, Paul; Committee Member: Zhou, Hao Min. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Hardie, Christopher David. "Micro-mechanics of irradiated Fe-Cr alloys for fusion reactors." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:a3ac36ba-ca6f-4129-8f37-f1278ef8a559.
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In the absence of a fusion neutron source, research on the structural integrity of materials in the fusion environment relies on current fission data and simulation methods. Through investigation of the Fe-Cr system, this detailed study explores the challenges and limitations in the use of currently available radiation sources for fusion materials research. An investigation of ion-irradiated Fe12%Cr using nanoindentation with a cube corner, Berkovich and spherical tip, and micro-cantilever testing with two different geometries, highlighted that the measurement of irradiation hardening was largely dependent on the type of test used. Selected methods were used for the comparison of Fe6%Cr irradiated by ions and neutrons to a dose of 1.7dpa at a temperature of 288°C. Micro-cantilever tests of the Fe6%Cr alloy with beam depths of 400 to 7000nm, identified that size effects may significantly obscure irradiation hardening and that these effects are dependent on radiation conditions. Irradiation hardening in the neutron-irradiated alloy was approximately double that of the ion-irradiated alloy and exhibited increased work hardening. Similar differences in hardening were observed in an Fe5%Cr alloy after ion-irradiation to a dose of 0.6dpa at 400°C and doses rates of 6 x 10-4dpa/s and 3 x 10-5dpa/s. Identified by APT, it was shown that increased irradiation hardening was likely to be caused by the enhanced segregation of Cr observed in the alloy irradiated with the lower dose rate. These observations have significant implications for future fusion materials research in terms of the simulation of fusion relevant radiation conditions and micro-mechanical testing.
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Zhang, Tao. "Laser surface hardening of AISI 1518 alloy steel." Thesis, Nelson Mandela Metropolitan University, 2010. http://hdl.handle.net/10948/723.
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The laser surface hardening process will enhance the hardness profile of automotive components and ensure better process control and predictability of quality as compared to the conventional hardening processes. A 2KW Nd-YAG laser system was used to harden the surface of alloy steel with various process parameters (laser power, focal spot diameter and beam velocity). The results (microhardness, microstructure change and residual stress distribution) were measured and analyzed with Vickers microhardness tester, optical/electron microscope and hole-drilling residual stress equipment. Statistical analyses of the experimental data were used for explaining the relationships between process parameters, microhardness and microstructure. General thermal hardening was applied in the research to show the influence of heating temperature and cooling method on microstructure and mechanical properties. Also, the results were compared with laser surface hardening process from microhardness, microstructure and residual stress to show the advantage of laser surface hardening. Through analysis of the results of the laser surface hardening experiments, a suitable laser power density and interaction time for optimum hardening was obtained. The presented laser surface hardening process can also be applied to other alloy steel surface hardening process.
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Rueff, Jean-Pascal. "Dichroisme circulaire magnétique des rayons X dans les systèmes terre rare - métal de transition : une nouvelle approche pour l'étude des propriétés magnétiques." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10034.
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Le dichroisme circulaire magnetique des rayons x (xmcd) est la difference des sections efficaces d'absorption des materiaux ferro- ou ferrimagnetiques, pour les deux polarisations circulaires de la lumiere. Le xmcd est selectif de l'espece chimique et de l'etat final sonde, par choix du seuil d'absorption. Notre etude porte sur les systemes terre rare - metal de transition, elabores au laboratoire l. Neel. Les poudres la(ni#xco#1#-#x)#5 et tb(ni#xco#1#-#x)#5 et les films amorphes gd-ni-co, ont ete etudies par xmcd, aux seuils l#2#,#3 de la terre rare. Dans ces composes, la variation de l'amplitude du dichroisme avec la teneur en co, peut se decrire dans un unique modele phenomenologique prenant en compte la polarisation de la bande 5d par l'hybridation 3d-5d et la dependance en spin de la partie radiale des elements de matrice dipolaires, due a l'echange 4f-5d. Les signaux geants, observes dans gd-ni-co, resultent de l'anisotropie magnetique, perpendiculaire au plan du film. Le xmcd aux seuils m#4#,#5 des terres rares et l#2#,#3 des metaux de transition, dans les monocristaux de hoco#2 et tbni#5 et dans les films minces amorphes er-fe, a permis l'etude en champ et en temperature du magnetisme 4f et 3d. Dans er-fe, nous avons mis en evidence une transition induite sous champ vers une structure magnetique cantee, prevue dans les modeles theoriques des systemes sperimagnetiques, autour du point de compensation. Les mesures sur les monocristaux ont confirme la sensibilite du dichroisme, detecte en rendement total d'electrons, a l'etat de surface des echantillons. Enfin, les calculs de diffusion multiple, realises au seuil k du co dans les composes r-co, ont montre que le signal de xmcd est correle au couplage spin-orbite dans la bande 5d de la terre rare, via l'hybridation 4p(co)-5d(r)
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Ghidini, Massimo. "Étude de systèmes magnétiques nanostructurés préparés par irradiation d'ions lourds de haute énergie." Université Joseph Fourier (Grenoble ; 1971-2015), 1995. http://www.theses.fr/1995GRE10198.
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Une methode originale d'elaboration de systemes magnetiques nanostructures a ete developpee: elle consiste a bombarder d'ions lourds rapides une cible cristalline. Dans certains cas, un ion lourd rapide traversant un materiau cristallin laisse sur son passage une nanocolonne amorphe, appelee trace latente. Le diametre des traces latentes est en general compris entre 2 et 7 nm, selon l'energie de l'ion incident et le type de cible. L'irradiation des films minces par des ions lourds de haute energie permet donc d'obtenir des materiaux tres inhomogenes a l'echelle nanoscopique. Dans ce travail, differents types de composes ont ete irradies pour obtenir des effets magnetiques originaux lies a ces microstructures. Les materiaux choisis, des composes de cobalt et d'une terre rare (rco#2 et rco#3, avec r=y,ce,tm), ont la particularite d'avoir des proprietes magnetiques differentes dans l'etat cristallin et dans l'etat amorphe. Certains sont uniquement ferromagnetiques dans l'etat amorphe, d'autres ont des temperatures d'ordre tres differentes suivant leur etat. Des traces amorphes de quelques nanometres de diametre sont creees par irradiation dans les alliages yco#2, yco#3, ceco#3. Les proprietes magnetiques de ces materiaux nanostructures sont ensuite analysees. Un mecanisme original de reinversement de l'aimantation a ete mis en evidence dans les compose yco#2 irradie. Un effet interessant de couplage magnetique particulier (appele effet de spring-magnet) du aux tailles nanometriques des nanocolonnes est observe dans le compose ceco#3 irradie
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OLIVEIRA, RENE R. de. "Estudo do efeito da tensão residual na microdeformação da rede cristalina e no tamanho de cristalito em aço Cr-Si-V jateado com granalhas de aço." reponame:Repositório Institucional do IPEN, 2016. http://repositorio.ipen.br:8080/xmlui/handle/123456789/27497.
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No presente trabalho foram estudados alguns efeitos causados pelo jateamento por granalhas no aço Cr-Si-V, processo que tem por objetivo aumentar a resistência à fadiga. Para este estudo a variação de parâmetros no processo são ferramentas para melhor compreender os mecanismos que influenciam esta propriedade. Os parâmetros utilizados neste trabalho foram a variação da granalha e o pré tensionamento das amostras aplicados em lâminas utilizadas em feixe de molas automobilísticas de aço de liga cromo silício vanádio (SAE 9254+V). Inicialmente foi realizada a avaliação do perfil de tensão residual, efetuada por difração de raios-x pelo método do sen2 ao longo da espessura na região onde a tensão é compressiva. Nos resultados nota-se um efeito anômalo em relação ao perfil característico da distribuição de tensão residual com a perda de compressão nas camadas iniciais em relação à superfície jateada. Com o uso da microscopia eletrônica de varredura foi observado a região afetada pelo jateamento por granalhas notando que as regiões plasticamente deformadas se encontram nas mesmas regiões onde ocorre a diminuição da tensão residual compressiva. O perfil obtido pela difração de raios-x fornece as informações necessárias com o propósito de conjugar os efeitos que a microtensão (microdeformação) influenciam na macrotensão (tensão residual). Esta relação foi comprovada pela sobreposição dos resultados encontrados na distribuição da microdeformação da rede cristalina com a tensão residual ao longo da espessura na região plasticamente deformada. Os resultados dos perfis das difrações de raios-x mostraram a existência de anisotropia de tensões entre os planos, geradas por defeitos de empilhamento e pela densidade de discordâncias. Assim sendo, para obter os valores das microtensões devem ser considerados os fatores das constantes elásticas (conforme o módulo das direções) e dos planos cristalográficos. O método aplicado foi o Williamson-Hall modificado. Além deste método outros também foram utilizados, tais como: método de Warren-Averbach e o método Single Line, este aplicando a série de Fourier, porém, ao observar os resultados, nota-se a diferença entre os valores obtidos nas deformações, tanto aos métodos quanto aos planos cristalográficos, porém a ênfase deste trabalho foi dada às características dos perfis da distribuição e não aos valores absolutos. Somando a isto, foi proporcionado o estudo da distribuição do tamanho médio de cristalito ao longo da espessura no perfil das difrações de raios-x e os resultados mostraram que esta distribuição varia de forma inversa a microdeformação. A relação entre o tamanho médio de cristalito e a variação das distâncias interplanares corresponde diretamente a alterações das densidades de discordâncias ocorridas no material que por sua vez estão ligadas às microdeformações da rede cristalina. Como complemento ao trabalho foram analisados o fator de concentração de tensão e ensaios de fadiga do material. O fator de concentração de tensão não variou conforme a utilização das granalhas S330 e S390, ambas sendo aplicadas no mesmo regime de jateamento. Os ensaios de fadiga indicaram que o pré tensionamento aumenta a vida útil nas tensões cíclicas do material estudado.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Xu, Sen. "Characterisation of radiation damage in Fe-Cr-Alloys." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534015.
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Song, Shenhua. "Radiation-induced grain boundary segregation in dilute alloys." Thesis, Loughborough University, 1995. https://dspace.lboro.ac.uk/2134/10475.
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Modelling of irradiation-induced segregation or thermal non-equilibrium segregation needs data on the impurity-point defect binding energy. These values are generally unavailable. In this work, an initial approach to determining impurityinterstitial binding energies in metals is established with some success on the basis of strain field arguments and the earlier work is slightly modified for more accurate calculations of oversized impurity-vacancy binding energies. The method is applied to predictions of various impurity-point defect binding energies in several transition metal matrices. With the aid of the predictions, some experimental results on radiation-induced segregation are reasonably satisfactorily interpreted. A radiation-induced grain boundary segregation (RIS) model is established for dilute alloys based on the complex mechanism and combined with McLean's equilibrium segregation model. In the model, radiation-enhanced solute diffusion is taken into consideration. Theoretical predictions are made for segregation of phosphorus in the neutron-irradiated a-Fe matrix. There exists a segregation transition temperature below which combined radiation-induced non-equilibrium and radiation-enhanced equilibrium segregation is dominant, and above which thermal equilibrium segregation is dominant; peaks in the temperature dependence of segregation shift to lower temperatures with decreasing neutron dose rate and/or increasing neutron dose; the combined radiation-induced non-equilibrium and radiation-enhanced equilibrium peak segregation temperature and the thermal equilibrium peak segregation temperature are about 150 and 550°C, respectively, for phosphorus grain boundary segregation in the a-Fe matrix at neutron dose rate = 10-6 dpa/s and neutron dose = I dpa . Grain boundary segregation of solutes in the neutron-irradiated and unirradiated (thermally aged) 2.25Cr1Mo steels doped with P and Sn is examined by means of field emission gun scanning transmission electron microscopy (FEGSTEM) which has very high spatial resolution (- 1 nm). The material is irradiated to a dose of 0.042 dpa at a dose rate of 1.05 x 10-8 dpa/s in a swimming pool-type light-water research reactor in the Paul Scherrer Institute (PSI) of Switzerland. Grain boundary microanalysis is performed in the Nuclear Electric Berkeley Technology Centre of the UK. Comparison of the experimental and predicted results shows that the predictions are generally consistent with the observations.
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Xu, Alan. "Atomic scale characterisation of radiation damage and radiation induced precipitation in tungsten-rhenium alloys." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:1ae33661-c81f-4e77-a80c-bc12ed9123d9.
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Tungsten is considered the prime candidate material for plasma facing components within fusion reactors. However, exposure of tungsten to neutron flux brings about transmutation of tungsten into by-products: Re, Os and Ta. Under increasing levels of radiation damage, irradiation induced clustering/precipitation takes place that embrittles and thus reduces lifetime of such tungsten components. This thesis was undertaken to explore this subject on a deeper level. There are three components to this study. The first part considers the effect of Re content on irradiation induced clustering. Lab-made plate W-xRe (x: 2, 5, 10 and 25at.%) alloys were exposed to 1.2, 3.9 and 33dpa, self-ion irradiated at 773K. Analysis of cluster number density and volume fraction found they increase with damage level and bulk Re content. Based on these trends and existing literature data, a hypothesis was proposed suggesting clusters originate from vacancy clusters. Also, at 33dpa, rod shaped clusters form in W-25Re alloys while spherical clusters are present in other alloys. The clusters show close correspondence with irradiation induced precipitates and appear to be precursor phase. In the second part of this thesis, the effect of Os and Ta on cluster formation and alloy mechanical properties is examined. Lab-made plate W-1Re-1Os and W-2Re-1Ta alloys were irradiated at 33dpa at 573 and 773K and compared against control W-2Re alloy. At 33dpa and 573K, the Os and Ta presence suppresses cluster formation. Both ternary alloys contain smaller cluster diameter, composition, number density and volume fraction than the W-2Re alloy. However, at 33dpa and 773K, Os and Ta have opposing effects on cluster behaviour. Os increases the cluster nucleation rate and raises irradiation hardening (compared to W-2Re). Meanwhile, Ta presence decreased cluster number density and reduced the irradiation hardening (compared to W-2Re alloy). As well, Ta showed no evidence of clustering, only Re clusters form in the W-2Re-1Ta alloy. The final aspect of the thesis analyzes the effect of material microstructure and external variables on cluster formation in W-Re alloys. Commercial wire form W-25Re alloy was irradiated at 1.2dpa at 573 and 773K as atom probe needles and bulk sample. The larger free surface on atom probe needle samples appears to act as a sink for self-interstitials and vacancies at both temperatures. The effect of grain size and dislocation density was examined by irradiating commercial W-5Re wire (0.5-1μm diameter) and plate (1-3mm diameter) samples (annealed and unannealed) to 33dpa and 573K. It was found grain boundaries and dislocations act as defect sinks at 573K. Additionally, radiation enhanced Re grain boundary enrichment was observed for first time. The effect of grain size on cluster behaviour at 773K was also analysed. Commercial wire and lab-made plate W-3Re, W-5Re and W-25Re alloys were irradiated to 33dpa at 773K. The larger grain boundary area in wire samples is suspected of acting as a sink for self-interstitials leaving more vacancies for promoting cluster formation compared to lab-made samples. The discoveries made in this thesis broaden our current understanding of irradiation induced phase formation in tungsten. Their implications on plasma facing component design are discussed as well as recommendations for improvements. Further, areas requiring further research in this field are also highlighted.
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Baumer, Richard E. (Richard Edward). "Atomistic simulations of radiation damage in amorphous metal alloys." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/88363.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 121-131).
While numerous fundamental studies have characterized the atomic-level radiation response mechanisms in irradiated crystalline alloys, comparatively little is known regarding the mechanisms of radiation damage in amorphous alloys. Knowledge of collision cascade dynamics is lacking, both with respect to the possibility of sub-cascade formation and concerning the types of damage created in individual cascades. This Thesis resolves these knowledge gaps through a systematic simulation study of the radiation response of amorphous metal alloys. Using a molecular dynamics simulation of /2 MeV ion irradiation in a realistic 2 billion-atom molecular dynamics simulation in amorphous Cu₅₀Nb₅₀, I show that radiation creates isolated nanometer-scale zones with rapidly quenching liquids. Quenched liquids reach large pressures and emit stress pulses that trigger polarized plastic deformation in adjacent material. In order to identify liquid zones in irradiated amorphous Cu₅₀Nb₅₀, I use molecular dynamics simulations to characterize the properties and glass transition temperature of uniform liquid Cu-Nb alloys. I show that radiation-induced liquid zones rapidly quench to material with the same properties as a uniform liquid quenched at an equivalent quench rate approaching 1014 K/s. These "super-quenched zones" (SQZs) are approximately 10 nm in diameter and provide a mechanistic explanation for radiation-induced swelling and ductilization in metallic glasses. The identification of plasticity adjacent to SQZs is an unexpected damage mechanism that could prove a limiting factor for the application of amorphous alloys in radiation environments. To aid selection of amorphous alloys with resistance to collision-induced plasticity, I formulate a micro-mechanical model for collision-induced plasticity in irradiated metallic glasses. The analytical model successfully ranks the damage-resistance of irradiated Cu- Nb alloys and should enable selection of amorphous alloys with optimized radiation tolerance. Finally, through characterization of quenched Cu₅₀Nb₅₀, I reveal that glass transition in Cu₅₀Nb₅₀ occurs by gelation due to formation of a mechanically stiff, percolating network of atoms with icosahedral local packing at the interfaces between compositionally enriched regions. These features of glass transition are similar to gelation processes in polymeric and colloidal gels and suggest new approaches for understanding glass transition in bulk metallic glasses.
by Richard E. Baumer.
Ph. D.
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NISHINO, YOICHI, SHINYA YAGI, MASAHIKO KATO, MANABU INUKAI, TAKAHIRO MOCHIZUKI, KOJI YAMAMOTO, HIDETOSHI MIYAZAKI, and KAZUO SODA. "SYNCHROTRON RADIATION PHOTOELECTRON STUDY OF HEUSLER-TYPE Fe2VAL-BASED ALLOYS." World Scientific Publishing, 2008. http://hdl.handle.net/2237/20772.
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Flores, Carlos D. (Carlos Daniel). "Evaluation of radiation induced segregation in Fe-Ni-Cr alloys." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/44597.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994.Includes bibliographical references.
by Carlos D. Flores.
M.S.
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Yi, X. "Electron microscopy study of radiation damage in tungsten and alloys." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:cb416551-164d-4290-b134-83278708ceff.
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The displacement damage induced by primary recoils of fusion neutrons in tungsten and alloys has been studied with self-ion irradiations, followed by damage characterization with electron microscopy. Tungsten and alloys (≤ 5 wt.% Re, Ta, V) were implanted with 2 MeV W+ ions over a dose range of 3.3×1017 - 2.5×1019 W+m-2 at temperatures ranging from 300 to 750°C. Dislocation loops of b = ½<111> (> 60%) and b = <100> were identified, and that ½<111> loops were found more thermally stable. Among loops that were large enough for nature determination, at least 50% were found to be of interstitial type, with larger fractions in high-temperature and high-dose conditions. The diameter of loops did not exceed 20 nm, with the majority being ≤ 5 nm. The loop number density varied between 1022 and 1023 m-3. The effects of ion dose, irradiation temperature, composition and grain orientation on damage microstructure were investigated. In-situ irradiations (150 keV W+ ions) were carried out as a complement to the bulk implantations. Qualitative trends in loop size, geometry and nature with irradiation dose and temperature were similar to bulk irradiated specimens. Also, the dynamics of defects and their effects on the damage evolution were explored. In-situ annealing of irradiated thin foils was performed to investigate the thermal stability of radiation damage in tungsten. The majority of microstructure transformations were completed within 15 min of annealing. However, extended durations did favour the increase of loop size and the fraction of ½<111> loops.
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Al, Tooq Zainab. "Simulating radiation damage in austenitic stainless steel and Ni-based alloys." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12599.
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The evolution of materials at an atomistic level may have vital consequences for the properties of materials. Therefore, modelling long time scale behaviour of defects in a material is very important, particularly for those used in nuclear power plants. The materials used in nuclear power plants should have good mechanical properties to overcome the corrosive environment and high temperature. Examples of these materials are the austenitic stainless steel and the Ni-based alloys due to their high temperature properties. Molecular Dynamics (MD) and on the fly Kinetic Monte Carlo (otf-KMC) techniques have been used to model the radiation damage in austenitic stainless steel and the Ni-based alloys. This thesis represents the main findings obtained. Three potentials were implemented and used to study radiation damage in austenitic stainless steel. Structural properties such as the elastic constants for the point defects in the pure metals were first calculated. This was followed by calculating the formation energies and migration energies of vacancy and self interstitial defects in the pure metals. Different calculations were performed using each potential on the ternary alloy (Fe with 10 at.% Ni and 20 at.% Cr) and the binary alloy (Ni with 20 at.% Cr) . For example, the segregation in these alloys was investigated using Monte Carlo simulations and results obtained for both alloys at high temperature MD. Furthermore, the vacancy formation energies were calculated for both alloys using all the potentials. Radiation damage at Grain Boundaries (GBs) in fcc Ni and a Ni-Cr binary alloy has been studied using MD and otf-KMC techniques. From the results obtained, the mobility of interstitials were found to be higher than that of vacancies and tend to move quickly to the GB. Vacancies are found to migrate to the GB if they are near otherwise they tend to form clusters in the bulk. During the simulations, interesting mechanisms were observed for the point defects migration and recombinations. Large roughening at the GB was observed, especially in the alloy system and overall the total number of defects accumulated on the GB after multiple collision cascades were relatively small. The radiation in fcc Ni resulting from low energy collision cascades was also modelled using MD and otf-KMC techniques. This part of work aimed replicating the observations seen in experiment and trying to understand them. Recombinations between vacancies and interstitials were found to happen from large distances with low barriers. Most defects produced from low energy collision cascades were found to recombine or interstitials were found to form clusters. Modelling the evolution of the vacancies shows the possibility of producing Stacking Fault Tetrahedra (SFT) which were found to dissociate at 200°C.
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Pareige, Philippe. "Etude à la sonde atomique de l'évolution microstructurale sous irradiation d'alliages ferritiques FeCu et d'aciers de cuve de réacteurs nucléaires." Rouen, 1994. http://www.theses.fr/1994ROUES070.
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Les aciers de cuve des réacteurs nucléaires sont fragilisés sous l'effet du bombardement neutronique. Parmi les causes possibles, le cuivre résiduel est reconnu pour jouer un rôle essentiel. Il est montré que la fragilisation est associée à une fine précipitation de particules riches en cuivre de taille nanométrique. Dans ce travail, nous avons, dans un premier temps, en utilisant les techniques de microscopie ionique, de sonde atomique classique et de sonde atomique tomographique, caractérisé (taille, densité, composition, nature des interfaces) les précipités formés sous une irradiation aux électrons (3 MeV, 300° C) et sous une irradiation aux neutrons (5,5 10#1#9n. Cm-2, e>1 MeV, 300°C), dans des alliages FeCu fortement (1,4 % pds) ou faiblement (0,1 % pds) sursaturé. La précipitation du cuivre est observée dans les différents cas. Toutefois, les caractéristiques de ces particules diffèrent, en termes de compositions et d'interfaces, selon les conditions d'irradiation et les teneurs nominales des alliages. Par ailleurs, avec les mêmes techniques expérimentales, l'étude d'un acier de cuve de centrale nucléaire française, irradie dans des conditions réelles de fonctionnement, a révélé la formation d'enrichissement locaux (3 nm) de la solution solide ferritique en atomes de Cu, Ni, Mn et Si. Sur la gamme des fluences étudiées, la taille et la composition chimique de ces amas restent inchangées. Cependant leur densité augmente avec la fluence. Une corrélation directe lie la présence de ces particules, dans lesquelles le cuivre apparaît jouer un rôle déterminant, et la fragilisation. En parallèle à ces travaux expérimentaux, les processus de germination et croissance sous irradiation aux neutrons dans les solutions solides sursaturées en cuivre sont discutés
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Chahal, Singh. "Biological effects of tarahertz radiation." Thesis, University of Reading, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493749.
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This thesis is an investigation of the biological effects of terahertz (THz) radiation at non-thermal power levels. One may loosely define the THz region of the electromagnetic spectrum spanning a range of frequencies between 0.1 and 10 THz. Recent advances in methods of generation and detection have made it possible to build instruments and perform experiments in this relatively unexplored part of he spectrum. Water represents an important constituent of biological systems and strongly absorbs in this frequency range. As a consequence, irradiation at THz frequencies can raise the temperature of biological material and temperature dependent processes can be influenced. THz radiation is non-ionising, with associated photon energies close to the thermal energy level of a metabolically active biological entity. At low power levels, however, a non-linear bio-effect relating to energy transfer from the field to the organism, which is not associated with a temperature rise, may be observed at specific frequencies. The current understanding of the interaction between THz radiation and biological material is. therefore, discussed within the framework of dielectric theory and is considered at both the macroscopic and microscopic levels. A discussion of important biological molecules, cells, tissues and a range of cellular processes is developed within this framework and the complexity of an interaction within a biological system is defined.
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Seddon, Gavin M. "Radiation effects on biochemical systems." Thesis, University of Salford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313912.
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Braddock, M. "Effects of radiation on DNA." Thesis, University of Salford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356177.
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Siam, Fuaada Mohd. "Modelling effects of ionising radiation." Thesis, University of Strathclyde, 2014. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=23162.
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In this thesis, we are concerned with the molecular biology processes of ionising radiation (IR) damage and its repair. In particular, we develop a mechanistic model of high dose irradiation damage to DNA in mammalian cells by considering a population of cells structured by the number of double strand breaks and mis-repairs. This framework allows us to construct a mechanistic explanation for the Linear-Quadratic (LQ) formalism. Other contributions of this thesis are a model of ataxia telangiectasia mutated (ATM) dynamics in DNA damage repair, and a discussion of bistability, an important ingredient in the construction of a general theory of non-targeted radiation effects.
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Wahle, Peter Joseph 1961. "Radiation effects on power MOSFETs under simulated space radiation conditions." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277024.
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Application of power MOSFETs in spaceborne power converters was simulated by exposing devices to low-dose-rate ionizing radiation. Both radiation-hardened and nonhardened devices were tested with constant and switched gate biases during irradiation. In addition, some of the devices were under load. The threshold-voltage shifts were strongly bias dependent. The threshold-voltage shift of the nonhardened parts was approximately dose-rate independent, while the hardened parts exhibited significant dose-rate dependence. A pre-anneal dose-rate dependence was found for the interface-state buildup of the switched and positively biased devices, but the results for the switched devices were qualitatively different than those for the positively biased devices. The buildup of interface trapped charge was found to be the primary contributor to mobility degradation, which results in reduced drive capability and slower operation of the devices. These results indicate that new methods need to be utilized to accurately predict the performance of power MOSFETs in space environments.
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Panagos, Panagiotis. "Characterising precipitate evolution in high temperature cast aluminium alloys using synchrotron radiation." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/characterising-precipitate-evolution-in-high-temperature-cast-aluminium-alloys-using-synchrotron-radiation(905742e7-5785-4b67-bdc6-67c781480941).html.
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Novel casting alloys that retain their mechanical strength at temperatures up to 300 °C are needed in order to improve automotive engine efficiency. The addition of Zr and V is a promising combination as a means of introducing the thermally stable cubic Al3ZrxV1-x nano-precipitates. In this project, the evolution of the Al3ZrxV1-x precipitates in multi-component cast aluminium alloys was characterised in a statistically significant way using small-angle X-ray scattering (SAXS). Unlike established metallurgical techniques, such as transmission electron microscopy (TEM), SAXS measures billions of precipitates in a single experiment. Two Al-6.8Si (wt.%) alloys were employed. One contained 0.30 wt.% Zr and 0.30 wt.% V and the other 0.37 wt.% Zr and 0.34 wt.% V. The alloys were cast and isothermally aged at 400 °C for times ranging from 3 to 50 h. Synchrotron SAXS was undertaken at the Diamond Light Source (DLS). Direct evaluation methods of SAXS spectrum were employed in order to extract information about the average precipitate size, precipitate size distribution and their evolution with ageing time. These results were compared with the results provided via TEM, both validating the methodology, and demonstrating the benefits and drawbacks of SAXS.From the SAXS analysis, the Guinier radius, Rg, was found to increase with ageing time from around 2 nm at 3 h to approximately 9 nm at 50 h. Precipitate volume fraction also increased from 0.11 vol.% to 0.24 vol.% for the lower solute alloy and from 0.14 vol.% to 0.33 vol.% for the higher solute one. In both alloys, the precipitate number density was observed to continuously decrease with ageing time. For the higher solute alloy, the average precipitate radius from the TEM measurements was found to be consistently smaller than Rg. Such a study is important because it extends the experimental SAXS methodology previously used only in simplified alloys to multi-component cast alloys of industrial importance. Moreover, the findings from this investigation suggest that both alloys quickly enter a stage where the precipitate growth and coarsening overlap, and the precipitate number density continuously decreases with time. Finally, this study underlines the importance of preliminary SAXS data treatment and provides an analytical guide in order to successfully characterize low volume fraction of precipitates in multi-component cast alloys.
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Tappin, David Keith. "The characterisation of displacement cascades in austenitic Fe-Cr-Ni alloys." Thesis, University of Liverpool, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317254.
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Andrade, González Neivi Rocío. "Aging effects in 319-type alloys." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102477.
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The present work was performed on primary A319.2 alloy to investigate the effect of magnesium and strontium additions on the heat treatment behaviour and mechanical properties of the alloy. Samples were cast in permanent mould, then cut in order to obtain coupons which were solution heat treated at 495°C for 4 and 24 hours, followed by quenching in hot water. Two different artificial aging temperatures were applied at 180°C and 220°C for times from 0.5 h up to 24 hours. The investigation consisted of a systematic measurement of macrohardness and matrix microhardness of samples under different heat treatment conditions. Tensile properties were also measured and electron microscopy study of critical samples was done.It is seen that the alloy does not exhibit the common peak-overaged aging conditions due to the presence of several coexisting phases. It was found that multiple aging peaks are present in the age-hardening curves of Al-Si-Cu-Mg alloys. From the scanning electron microscopy studies, it is seen that addition of magnesium (~0.40 wt%) leads to the precipitation of coarse A1 5Mg8Si6Cu2 particles. Strontium modification of the high magnesium alloys leads to segregation of Cu-intermetallics in areas away from the growing Al-Si eutectic regions. It was found that strontium modification retards the precipitation of the silicon out of the matrix.
The effect of aging time and temperature on the structure of the age-hardening precipitates was studied with TEM. TEM observations reveal that the age-hardening behavior is related to the precipitation sequence of the alloy. For the Al-Si-Cu-Mg alloy, the first aging peak is the result from the high-density GP zones, while the subsequent are from metastable phases. The transition from GP zones to metastable phases may be the main reason for the formation of multiple aging peaks.
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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.
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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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Spaargaren, Susan Marianne Rosemary. "Radiation effects on silica based waveguides." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267942.
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Hasan, N. M. "Effects of ionizing radiation on biomolecules." Thesis, University of Salford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234702.
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Barbary, O. M. "Effects of ionizing radiation on lipids." Thesis, University of Salford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372135.
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Harris, Rhodri. "Radiation effects on custom MOS devices." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301376.
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Inayat, Hussain Husnain. "Thermoviscous effects in acoustic radiation problems." Lyon, INSA, 2009. http://theses.insa-lyon.fr/publication/2009ISAL0124/these.pdf.
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La science et la technologie ont une influence croissante sur notre vie quotidienne. On peut désormais s’imaginer voir le monde uniquement à travers le prisme d’un ordinateur. Ainsi, nous nous retrouvons asservis par la technologie moderne. Cette unique perspective, celle du progrès technologique, possède ses avantages et ses inconvénients. L’un des sousproduits indésirables de l’évolution technologique et industrielles est la pollution, et notamment la pollution sonore. Le bruit est et a toujours été un défi dans de nombreux secteurs industriels, tels que l’aéronautique ou l’automobile. Ce problème se pose surtout par l’utilisation de matériaux de plus en plus légers et performants. Toutefois, les vibrations d’une structure ont tendance à augmenter avec la légèreté du matériau utilisé, ce qui peut conduire à des niveaux de bruits importants, dans la mesure où le bruit rayonné par une structure est directement lié à ses vibrations. Pour réduire ces nuisances, les chercheurs et les ingénieurs ont développé différents moyens parmi lesquels : 1. Le contrôle du bruit actif, 2. La réduction du bruit à travers les matériaux absorbants, 3. La réduction du bruit en utilisant des fluides viscothermique. La présente thèse est basée sur l’utilisation des caractéristiques thermovisqueuse des fluides afin de réduire les niveaux de bruits générés par les structures. Différentes configurations ont été définies sur plusieurs cas pour démontrer l’efficacité des propriétés thermovisqueuses du milieu fluide dans la réduction du bruit. Les configurations étudiées ici restent simples, afin de mettre l’accent sur la recherche de tendances générales plutôt que sur la résolution de problèmes industriels complexes. L’étude se limite essentiellement aux structures régulières, bien que les fluides soient étudiés de manière plus globale. Un modèle général de fluide est introduit, permettant ainsi d’examiner n’importe quel milieu, pourvu que les caractéristiques du fluide soient connues. Le modèle proposé dans cette thèse repose sur la résolution simultanée du système complet des équations de Navier-Stokes qui de fait est fondamentalement différent des méthodes de résolution standards. Une solution tridimensionnelle est obtenue en utilisant des opérateurs différentiels modifiés. Ce modèle est tout d’abord appliqué à une plaque seule, puis à une double paroi. Les résultats théoriques sont encourageants, puisqu’ils mettent en évidence un gain considérable en matière d’isolation acoustique grâce à l’utilisation de milieux thermovisqueux. Les résultats pour de l’air et de l’eau sont ainsi présentés. Une validation expérimentale a aussi été réalisée. Les différences entre théories et expériences sont présentées et expliquées dans le texte. Pour finir, un modèle original de plaque équivalente est introduit. La méthode présentée s’appuie sur des fluides à très fortes viscosité comme les huiles Rhodorsil R 47. La méthode est basée sur une approche asymptotique, qui est considérablement plus simple que la résolution complète des équations de Navier-Stokes. Il a été montré que de forts facteurs d’amortissement sont obtenus en employant cette technique. Enfin, la comparaison des résultats permet de monter un réduction significative des niveaux de bruits rayonnéThe world we live in, is constantly changing under the influence of science and technology. The modern day technology has enslaved us in such a manner that now one may imagine leading a life simply by sitting in front of a personal computer and getting all things done from there. This “one window”operation, in other words the technological advancement, has its own advantages and disadvantages. One of the unwanted byproduct of the technological and industrial development is pollution. One of the major forms of pollution is NOISE. Noise is and has always been the challenge for many industries such as aircraft and automobile industries. This problem arises with the use of more efficient and light weight materials. The lighter the material, the more the vibration. Since noise is directly related with the vibration of the structure, hence more vibration implies higher noise. Scientist and engineers have devised ways in order to stand up to this menace. Three methods are identified in general: 1. Active Noise Control 2. Noise Reduction through Absorbing Materials 3. Noise Reduction using Thermoviscous Fluids The main theme of this thesis is based on the last method. The present work deals with the thermoviscous characteristics of the fluids in reducing the radiated noise levels. Various configurations with varying cases have been considered to demonstrate the effectiveness of thermoviscous properties of the medium in noise elimination. The configurations studied are essentially kept simple and emphasis is rather put on finding the trends than solving complicated industrial problems. By and large, the investigation is limited to only regular structures, however, the fluids are studied in a comprehensive manner. A general fluid model is introduced which permits to examine any medium, provided the characteristics of the fluid are known. The proposed model relies on the simultaneous solution of the full set of Navier Stoke’s equations and hence is essentially different from the contemporary solution methods. A 3D solution is obtained using modified differential operators. This model is applied on the simple plates initially and later on the double wall panel. The theoretical results are encouraging in showing considerable gain in sound isolation with the use of thermoviscous media. Results for both air and water are shown. Experimental validation has been performed also. Differences are indicated in the text and appropriate reasons given. Before giving the conclusion, an innovative model of an equivalent plate is introduced. The method shown uses very high viscosity fluids such as Rhodorsil R 47 oils. The method is based on an asymptotic approach, which is considerably simpler than the full solution of the Navier Stoke’s equation. It has been shown that high damping factors are obtained using this technique. The method is accompanied by radiation result comparison which successfully indicates an incredible reduction in noise levels
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CARDOSO, LORENA M. "Avaliação da resistência a flexão de liga de titânio submetida a soldagens laser e TIG, visando a prótese dentária." reponame:Repositório Institucional do IPEN, 2007. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11636.
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Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia)
IPEN/D-MPLO
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo , Sao Paulo
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Walldén, Johan. "Radiation Induced Effects in Electronic Devices and Radiation Hardening By Design Techniques." Thesis, Linköpings universitet, Elektroniska komponenter, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-109343.
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The aim with this thesis has been to make a survey of radiation hardened electronics, explaining why and how radiation affects electronics and what can be done to harden it. The effects radiation have on electronics in general and in specific commonly used devices are explained qualitatively. The effects are divided into Displacement Damage (DD), Total Ionizing Dose (TID) and Single Event Effects (SEEs). The devices explained are MOSFETs, Silicon On Insulator (SOI) transistors, 3D-transistors, Power transistors, Optocouplers, Field Programmable Gate Arrays (FPGAs), three dimensional circuits (3D-ICs) and Flash memories. Different radiation hardening by design (RHBD) techniques used to reduce or to remove the negative effects radiation induces in electronics are also explained. The techniques are Annular transistors, Enclosed source/drain transistors, Guard rings, Triple Modular Redundancy (TMR), Dual Interlocked Storage Cells (DICE), Guard gates, Temporal filtering,Multiple drive, Charge dissipation, Differential Charge Cancellation (DCC), Scrubbing, Lockstep, EDAC codes and Watchdog timers.
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Gettens, Robert T. T. "Protein adsorption onto medical alloys voltage effects /." Related electronic resource:, 2007. http://proquest.umi.com/pqdweb?did=1398611421&sid=1&Fmt=2&clientId=3739&RQT=309&VName=PQD.
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Korojy, Bahman. "Volume Change Effects during Solidification of Alloys." Doctoral thesis, Stockholm : Skolan för industriell teknik och management, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10527.
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Fifer, Tommy L. "Radiation effects on multi-junction solar cells." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA401081.
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Thesis (M.S. in Electrical Engineering) Naval Postgraduate School, Dec. 2001.Thesis advisor(s): Michael, Sherif . "December 2001." Includes bibliographical references (p. 65-67). Also available online.
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Irvine, Peter J. "Climatic effects of solar radiation management geoengineering." Thesis, University of Bristol, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.573384.
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Geoengineering, intentional large-scale manipulation of the Earth-system, has been proposed as a means to ameliorate the impacts of global warming. There are two approaches; Carbon Dioxide Removal (CDR) geoengineering which would reduce C02 concentrations and address the cause of climate change, and Solar Radiation Management geoengineering which would cool the planet by reducing the amount of sunlight absorbed by the planet without affecting CO2 concentrations. This thesis reviews geoengineering and investigates the direct and indirect climate effects of SRM geoengineering. The sunshade geoengineering scheme, which would reduce the solar insolation, is investigated in depth in this thesis. Sunshade gcoenginecring may be implemented at a range of C02 concentrations and it would also offer control over the amount of insolation that reaches the planet. Both of these aspects of sunshade geoengineering are investigated using a climate model and it is found that sunshade geoengineering would ameliorate most of the effects of elevated C02 but would cause heterogeneous changes in climate; globally reducing precipitation and leaving many regions with a climate markedly different from the pre-industrial. The regional climate effects of sunshade geoengineering are found to vary linearly with both the solar insolation reduction and the C02 forcing applied. An off-line ice-sheet model is used to investigate the indirect climate effects of different strengths of sunshade geoengineering on the Greenland Ice-Sheet at quadrupled CO2 levels, to determine whether sunshade geoengineering could stabilize the ice-sheet and reduce sea-level rise. It is found that the ice-sheet would eventually collapse at quadrupled C02 levels but that strong sunshade geoengineering can stabilize the entire ice-sheet or at weaker implementations, part of the ice-sheet could be maintained. A comparison is made between the urban, crop and desert surface albedo geoengineering schemes, which would have a highly heterogeneous radiative forcing effect, and sunshade gcocngineering, which would have a more homogeneous radiative forcing effect. This comparison shows that regional geoengineering forcing, if it is relatively weak, may provide local and regional cooling and other benefits but for stronger land albedo forcing there are large shifts in precipitation, including substantial reductions in monsoon precipitation, which could prove to be more harmful than the effects of global warming. Finally, to determine the robustness of the results in this thesis, a perturbed parameter ensemble is developed, tested and then used to investigate the effects of parametric uncertainty on the sunshade geoengineering climate effects. The perturbed parameter results agree with much of what was found in other parts of the thesis about sunshade geoengineering but finds that there is uncertainty in the resid- ual warming at the poles, the magnitude of the northward shift of the ITCZ, and that the standard climate model may have overestimated the effectiveness of sunshade geoengineering at maintaining the Greenland Ice-Sheet. Overall, I find that SRM geoengineering could offer a considerable amelioration of the impacts of global warming; however, the climate would differ substantially from a low-C02 climate, and there would be winners and losers as a result. Regional SRM geoengineering would have very heterogeneous climate impacts, potentially causing large problems but could offer a large degree of control over the climate. 'Whether the political risks that control over the climate could bring would outweigh the potential climate benefits, is an open question.
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Holland, Andrew David. "Radiation effects in CCD X-ray detectors." Thesis, University of Leicester, 1990. http://hdl.handle.net/2381/27614.
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The outcome of several studies into future X-ray astronomy satellite missions has favoured the approach of using grazing incidence optics in conjunction with Charged Coupled Devices (CCD's) as focal plane detectors. This approach allows astrophysical investigation of unprecedented sensitivity by maximising source detectability and by resolving the source spectra. This thesis covers work performed in the development and evaluation of EEV CCD's for use as focal plane X-ray detectors. Due to the nature of the space environment, the interactions of radiation with CCD's also form a major part of this thesis. The subject of X-ray astronomy is introduced and the considerations affecting the operation of CCD's in space are discussed. The construction and operation of the CCD is thoroughly reviewed. The equipment and techniques used to evaluate the performance CCD's to X-rays are presented. A model is developed to simulate the interaction of X-rays with CCD's and this is followed by detailed measurements of X-ray performance. Further improvements to the design of CCDs to optimise their use as X-ray detectors are also discussed. These improvements include increased high and low energy quantum efficiency, larger area, low noise, reduced dark current and increased tolerance to radiation damage. Sources of background signal are investigated which lead to background rejection schemes for different CCD designs. Modelling is also performed to simulate an application of CCD's in space. Measurements of the radiation damage suffered by the CCD's are given and the damage mechanisms which will ultimately lead to device failure in space are discussed. The radiation damage covers irradiation using Co60 and heavy ions, but focuses on the effects of protons of doses below 5 krads. The impact of such a fluence on the scientific performance of an X-ray satellite is evaluated.
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Waters, R. D. "Effects of gamma radiation on biomedical polymers." Thesis, Liverpool John Moores University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378506.
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Bee, Sarah Caroline. "Radiation effects in analogue to digital converters." Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298887.
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Sweeney, Marion Carol. "The effects of gamma radiation on DNA." Thesis, University of Leicester, 1986. http://hdl.handle.net/2381/33943.
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