The power of the McCumber theory [D. E. McCumber, Phys. Rev. 136, A954-957 (1964)] consists in its ability to accurately predict emission cross section spectra from measured absorption, and vice versa, including both absolute values and spectral shapes. While several other theories only allow the determination of integrated cross sections, the McCumber theory is unique in generating the spectral shape of a cross section without any direct measurements regarding that cross section. The present work is a detailed study of the range of validity of the McCumber theory, focussing particularly on those aspects that most critically affect its applicability to transitions of rare earth ions in glasses. To analyze the effect of the spectral broadening on the accuracy of the technique, experiments were performed at room and low temperature. The theory was tested by comparing the cross sections calculated using the McCumber relation with those obtained from measurements. At room temperature, a number of ground state transitions of three different rare earth ions (Nd, Er and Tm) in oxide and fluoride glass hosts have been studied. Special attention was paid to the consistency of the measurements, using the same experimental setup, same settings and same detection system for both absorption and fluorescence measurements. Other aspects of the experimental procedure that could generate systematic errors, like fluorescence reabsorption and baseline subtraction uncertainties in the absorption measurements, were carefully investigated. When all these aspects are properly accounted for, we find in all cases an excellent agreement between the calculated and the measured cross section spectra. This suggests that the McCumber theory is not limited to crystalinne hosts, but describes quite well the reciprocity between emission and absorption for the broader transitions of rare earths in glassy hosts. This good agreement does not hold, however, for the low temperature results. The distortion observed in this case follows the theoretically predicted behavior, and corresponds to the amplification of the gaussian wings that describes the inhomogeneous type of broadening. Our results suggest that the McCumber theory must be used with caution for temperatures below 200 K.

Analyzing stellar spectra plays a big role in understanding the evolution of our galaxy. Having good data for spectral line properties is very important when analyzing these spectra. One part of the Gaia-ESO public spectroscopic survey (GES) is to gather data for spectral line properties from stellar spectra. The scope of this project is to study one of these properties, the spectral line width caused by collisional broadening by hydrogen. Collisional broadening by hydrogen occurs when a hydrogen atom collides with a particle. The goal of this project is to successfully calculate the collisional spectral line broadening of iron lines where new data is missing from the GES using modern quantum mechanical calculations. These calculations are done using the ABO theory, which is more advanced than previously established theory.A table of Fe-I (Neutral iron) spectral lines without collisional broadening data in the GES has been provided. Using the ABO theory and the accompanying ABO cross section calculator code, estimates of collisional broadening by hydrogen have been calculated for these lines. The new calculations predict that the line width of the spectral lines are typically twice as large compared to older estimates calculated using simpler theory. This new data can be expected to improve stellar spectrum analysis in the Gaia-ESO survey spectra. / Analys av stjärnspektran spelar en stor roll i vår förståelse av vintergatans utveckling. Att ha bra data för spektrallinjers egenskaper är oerhört viktigt vid analys av dessa spektran. En del i Gaia-ESO public spectroscopic survey (GES) är att samla in data för dessa spektrallinjers egenskaper ur stjärnspektran. Omfattningen av detta projekt innefattar att titta närmare på en av dessa egenskaper, spektrallinjebreddning orsakad av kollisionsbreddning av väte. Kollisionsbreddning av väte uppstår när en väteatom kolliderar med en annan partikel. Målet med projektet är att med framgång beräkna kollisionsbreddningen av spektrallinjer från järn där ny data saknas ur GES genom att använda moderna kvantmekaniska beräkningar. Dessa beräkningar är gjorda med den så kallade ABO-teorin, vilken är mer avancerad än tidigare etablerade teorier. En tabell med Fe-I (neutralt järn) spektrallinjer utan kollisionsbreddningsdata i GES har tillhandahållits. Med hjälp av ABO-teorin och den medföljande ABO-tvärsnittsräknar-koden har beräkningar av kollisionsbreddning med väte utförts för dessa linjer. De nya beräkningarna förutser att spektrallinjernas bredd blir typiskt två gånger så stor jämfört med de äldre beräkningarna gjorda med enklare teori. Denna nya data kan förväntas att förbättra analysen av stjärnspektrum ur Gaia-ESO kartläggningen.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 1975 / Vita. / Includes bibliographical references. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Physics

In disordered alloys, atoms belonging to the same chemical element will exhibit different environments. This leads to variations in the atoms’ local electronic structures, which in turn leads to variations in the binding energies of their core levels. These binding energies can be measured experimentally using core level X-ray photoelectron spectroscopy (XPS). Therefore, in theory at least, core level XPS can be used to resolve different environments in alloys. However, to make this a reality one must understand how an atom’s local electronic structure, and hence the binding energies of its core levels, are affected by local environment. In this thesis, two simple phenomenological models are explored which purport to correctly describe the local electronic structure of disordered alloys. The first model which we consider has its roots in chemical intuition; specifically, the notion that pairs of unlike atoms, i.e. atoms belonging to different chemical elements, transfer a certain quantity of charge, while like atoms do not. Using this model - known as the optimised linear charge model (OLCM) - the relationship between an atom’s local electronic structure, core level binding energies, and its environment is explored in detail, both in the bulk of disordered alloys and near their surfaces. As well as ‘homogeneous’ disordered alloys, in which the concentrations of the alloy’s constituent elements are the same throughout the entire alloy, various ‘inhomogeneous’ disordered alloy systems are considered. These include alloys exhibiting surface segregation - in which the concentrations at the surface differ from those in the bulk - as well as interfaces between two metals with various levels of intermixing. The results of our investigation of bulk inhomogeneous alloys are compared to analogous ab initio results, which confirms the model’s viability as a tool for rationalising the relationship between local electronic structure, core level binding energies, and environment. More generally, our results also reveal a number of interesting new phenomena. Firstly, the widths of spectra in inhomogeneous disordered alloys are significantly larger in some cases than is possible in any analogous homogeneous disordered alloy. Secondly, differences between the concentrations of each element at the surface and deep within the bulk cause a shift in the work function of the alloy under consideration. The latter results in qualitatively different trends than one would expect if this phenomenon was ignored, and prompts an alternative interpretation of the results of a recent experimental study. The second model which we consider is a particular case of the charge-excess functional model, in which the realised charges on all atoms are those which minimise a particular expression for the total energy of the system, and whose accuracy has been well established. The underlying assumptions and properties of this model are explored in detail, adding insight into the nature of the screening and inter-atomic interactions in disordered alloys. The model is shown to be equivalent to the OLCM for the case of binary alloys, and can therefore be considered to be the generalisation of the OLCM for alloys containing more than two chemical elements. The model is also used to derive analytical expressions for various physical quantities for any alloy, including the width of core level XPS spectra and the Madelung energy. These expressions are then used to investigate how the physical quantities to which they pertain vary with the concentrations of each element in a homogeneous disordered alloy consisting of three elements. Among other things, it was observed that the width of the core level XPS spectra is maximised when the concentrations of the two elements in the alloy with the largest electronegativity difference have equal concentrations, while the remaining element has a vanishing concentration.

No description available.

No description available.

Clad alloys feature one or more different alloys bonded to the outside of a core alloy, with non-equilibrium, interalloy interfaces. There is limited understanding of the recovery and recrystallization behaviour of cold rolled clad aluminum alloys. In order to optimize the properties of such alloys, new heat treatment processes may be required that differ from what is used for the monolithic alloys. This study examines the recovery behaviour of a cold rolled Novelis FusionTM alloy containing an AA6XXX core with an AA3003 cladding on one side. The bond between alloys appears microscopically discrete and continuous, but has a 30 m wide chemical gradient. The as-deformed structure at the interalloy region consists of pancaked sub-grains with dislocations at the misorientation boundaries and a lower density organized within the more open interiors. X-ray line broadening was used to extract the dislocation density from the interalloy region and an equivalently deformed AA6XXX following static annealing using a modified Williamson-Hall analysis. This analysis assumed that Gaussian broadening contributions in a pseudo-Voigt function corresponded only to strain from dislocations. The kinetics of the dislocation density evolution to recrystallization were studied isothermally at 2 minute intervals, and isochronally at 175 and 205°C. The data fit the Nes model, in which the interalloy region recovered faster than AA6XXX at 175°C, but was slower at 205°C. This was most likely caused by change in texture and chemistry within this region such as over-aging of AA6XXX . Simulation of a continuous annealing and self homogenization process both with and without pre-recovery indicates a detectable, though small change in the texture and grain size in the interalloy region. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-10-02 10:19:10.279

Um sistema de diagnóstico por espectroscopia no visível foi implantado no tokamak TBR-I. O diagnóstico consiste de um espectrógrafo (do tipo Czerny-Turner), um sistema de acoplamento óptico e um detetor multicanal (MCP). O diagnóstico foi usado para observar e identificar impurezas presentes no plasma do TBR-I. As principais impurezas observadas foram oxigênio (O-II) e nitrogênio (N-II). Foi feito um estudo no alargamento das linhas do hidrogênio e dos íons para se obter a temperatura a partir do efeito Doppler. As intensidades das linhas espectrais foram observadas de descarga em descarga. / A visible spectroscopic diagnostic was implemented on TBR-I tokamak. The diagnostic system consist of a 1,5 m spectrograph (Czerny-Turner type), an optical coupling system and a microchannel plate (MCP) detector. The diagnostic system was used to examine and document the impurity content of the plasma in TBR-I. The main impurities discovered were oxygen (O-II) and nitrogen (N-II). Line broadening experiments were performed on hydrogen and ions to obtain the temperatures using Doppler broadening effects. The intensities of the spectral lines were measured on a shot to shot basis.

Aplicações em ambientes expostos a elevados níveis de radiação ionizante impõem uma série de desafios ao desenvolvimento de projetos de circuitos integrados na tecnologia Complementary Metal–Oxide–Semiconductor (CMOS), uma vez que circuitos CMOS estão sujeitos às falhas transientes oriundas de radiação externa. Num circuito do tipo CMOS, as áreas sensíveis aos efeitos da incidência de partículas ionizantes são as regiões dreno-substrato reversamente polarizadas, existentes nos transistores em regime de corte (VARGAS; NICOLAIDIS, 1994). Com o avanço tecnológico e consequente diminuição das dimensões dos dispositivos semicondutores, estes efeitos degradantes tornam-se uma preocupação constante devido às menores características físicas dos transistores (WANG et al., 2007). Os circuitos integrados apresentam, durante a sua vida útil, um processo de degradação das suas características iniciais. Assim, a esse processo de degradação também chamamos de envelhecimento (aging). É um processo lento e cumulativo provocado por todos os mecanismos que acabam por alterar os parâmetros físicos e eléctricos dos circuitos, diminuindo o seu tempo de vida útil (FU; LI; FORTES, 2008). Dentre os efeitos de variabilidade temporal, os que mais têm causado interesse da comunidade científica são o Randon Telegraph Noise (RTN) com sua origem na atividade de traps (armadilhas) de interface e Single Event Transients (SET) com sua origem na radiação ionizante ao qual o circuito é exposto. Em relação aos efeitos de degradação destaca-se o efeito Bias Temperature Instability (BTI) (VALDUGA, 2012), que da mesma forma que o RTS, tem sua origem vinculada aos efeitos das traps.Modelos padrão para simulação elétrica de circuitos não levam em consideração os efeitos causados por armadilhas de cargas tais como Bias Temperature Instability (BTI) e Random Telegraph Noise (RTN). Tais variabilidades em nível de dispositivo podem causar perda de confiabilidade, como por exemplo, o surgimento de Propagation-Induced Pulse Broadening (PIPB). Conforme o escalonamento (scaling) tecnológico, a velocidade das portas lógicas aumenta e os SETs podem ser propagados através de circuito combinacional e, inclusive, sofrer alargamento, caso a largura do pulso transiente supere um valor mínimo crítico que depende da tecnologia (DODD et al., 2004), caracterizando assim um PIPB. Com base nisso, técnicas de injeção de falhas usadas em circuitos complexos não se mostram eficientemente previsíveis, levando a uma subestimativa da sensibilidade de circuitos à propagação de SETs. Com a utilização de um simulador elétrico que agrega a análise de BTI, temos melhores estimativas dos efeitos de PIPB na degradação de um circuito, que pode provocar violações de temporização em sistemas síncronos. Dessa forma, pode-se então trabalhar em uma projeção do circuito de forma a torná-lo mais robusto em relação aos efeitos de envelhecimento e na proteção às falhas transientes. Com base no que foi anteriormente apresentado, este trabalho analisa o comportamento de circuitos através de simulações elétricas de radiação ionizante, permitindo avaliações da suscetibilidade e confiabilidade de circuitos integrados aos efeitos de falhas transientes. Para a realização destes experimentos, foram realizadas simulações elétricas considerando-se os efeitos de envelhecimento. Para uma cadeia lógica de 2000 inversores sequencialmente dispostos na tecnologia 32nm pode-se prever que o pulso transiente está sujeito a um alargamento de sete vezes sua largura inicial no momento da incidência, para transistores em suas dimensões mínimas. A partir da proposta apresentada, pode-se determinar a possibilidade de alargamento ou atenuação de um SET ao longo do circuito de maneira eficiente para que as devidas precauções possam ser tomadas. / Applications in environments exposed to high levels of ionizing radiation impose a number of challenges for the development of integrated circuit designs in CMOS technology. CMOS circuits are vulnerable to transient faults from external radiation. In a CMOS circuit, areas sensitive to the effects of ionizing particle incidence are as reverse polarized drain-substrate regions in the transistors at cut-off (VARGAS; NICOLAIDIS, 1994). The technological advance and consequent downscaling of semiconductor devices, these degrading factors become a constant concern due to the higher vulnerability to transient faults (WANG et al., 2007). The integrated circuits have during their useful life a process of degradation of their initial characteristics. Thus, this process of degradation is also called aging. It is a slow and cumulative process caused by all the mechanisms that end up changing the physical and electrical parameters of the circuits, decreasing their useful timing life (FU; LI; FORTES, 2008). Among the temporal variability effects, the Randon Telegraph Noise (RTN) with its origin in the activity of traps (interface traps) and Single Event Transients (SET) with their origin in the ionizing radiation circuit is exposed. In terms of the effects of degradation, the Bias Temperature Instability (BTI) effect (VALDUGA, 2012) stands out, which, like the RTS, has its origin linked to the effects of the traps. Standard electrical simulation models do not take into account the effects caused by charged traps such as Bias temperature instability (BTI) and random telegraph noise (RTN). Such device-level variability can cause reduced reliability, for example, the Propagation-Induced Pulse Broadening (PIPB). According to the technological scaling, the speed of the logic gates increases and the SETs can be propagated through a combinational circuit and even may suffer broadening if the transient pulse width exceeds a critical minimum value that depends on the technology (DODD et al., 2004 ), characterizing a PIPB. Based on this, fault injection techniques in complex circuits are not efficiently in predicting, leading to an underestimation of circuit sensitivity to propagation of Single Event Transients (SETs). Using an electrical simulator that aggregates a BTI analysis, we have better estimates of PIPB effects on circuit degradation, which may lead to timing violations in synchronous systems. Then we can put effort in circuit design in order to make it more robust regarding to aging effects and transient faults protection. Based on what has been previously presented, this thesis analyzes the behavior of circuits through electrical simulations of ionizing radiation, allowing susceptibility and reliability evaluations of integrated circuits to the effects of transient faults using electrical simulations. For the accomplishment of these experiments, electrical simulations were performance considering the effects of aging. For a logic chain of 2000 inverters sequentially arranged in the 32nm technology it can be predicted that the transient pulse is subjected to a broadening of seven times its initial width at the time of incidence for transistors with minimum dimensions. From the analysis presented, we can evaluate the possibility of broadening or shrinking of SETs thought the circuit in an efficient way to improve radiation-hardening techniques.

Dans le Modèle Standard de la physique des particules, la théorie de l’interaction forte, la chromodynamique quantique (QCD), est une théorie de jauge de groupe de symétrie SU (Nc) par rapport au nombre quantique de couleur. QCD obéit à la propriété de liberté asymptotique, permettant le calcul d’observables physiques à haute énergie en utilisant la QCD perturbative (pQCD). Cette thèse traite de la description en pQCD des taux de production de hadrons dans les collisions hadroniques à haute énergie, en vue d’applications à la phénoménologie des collisions proton-noyau et noyau-noyau dans les collisionneurs de hadrons (RHIC, LHC), où des effets nucléaires (shadowing, perte d’énergie partonique, élargissement de l’impulsion transverse) entrent en jeu. Dans une première partie, j’étudie l’élargissement de l’impulsion transverse d’un système de partons énergétiques traversant un noyau, en mettant l’accent sur la structure de couleur du processus. Un cadre théorique basé sur le formalisme des dipôles est utilisé, et une équation cinétique est dérivée pour la distribution en impulsion transverse de la paire de partons, en demandant que cette paire soit dans un état de couleur donné (représentation irréductible de SU (Nc)) à la fois dans l’état initial et dans l’état final. La structure de couleur est codée dans un opérateur d’évolution de couleur, qui est obtenu pour tout type de paire de partons. Pour une paire compacte de petite taille, la dérivation donne une interprétation physique claire du processus d’élargissement de l’impulsion transverse. Dans une deuxième partie, je discute la matrice de dimension anormale Q, qui est formellement analogue à l’opérateur d’évolution précédent, et qui apparaît lors de l’ étude du rayonnement de gluons mous associé à une diffusion partonique dure 2 −> 2. Il a été remarqué que la matrice Q associée à gg −> gg a une symétrie surprenante (reliant les degrés de liberté externe et interne). J’ai développé des outils pour dériver les matrices Q associées à des diffusions 2 −> 2 impliquant des partons généralisés, afin d’explorer si la symétrie observée pour gg −> gg est fortuite ou non. / In the Standard Model of particle physics,the theory of the strong interaction, Quantum Chromodynamics (QCD), is a gauge theory of symmetry group SU (Nc) with respect to the color quantum number. QCD obeys the property of asymptotic freedom, allowing the computation of high-energy physical observables using perturbative QCD (pQCD). This thesis deals with the pQCD description of hadron production rates in high-energy hadronic collisions, in view of applications to the phenomenology of proton-nucleus and nucleus-nucleus collisions at hadron colliders (RHIC,LHC), where so-called nuclear effects (shadowing, parton energy loss, transverse momentum broadening) come into play. In a first part, I study the transverse broadening of an energetic parton system crossing a nucleus, putting emphasis on the color structure of the process. A theoretical setup based on the dipole formalism is used,and a kinetic equation is derived for the parton pair transverse momentum distribution, requiring the parton pair to be in a given color state (SU (Nc) irreducible representation) both in the initial and final state. The color structure is encoded in a color evolution operator, which is obtained for any type of parton pair. For a small-size compact pair, the derivation yields a transparent physical interpretation of the pair transverse broadening process. In a second part, I discuss the soft anomalous dimension matrix Q, which is formally analogous to the previous evolution operator, and which appears when studying soft gluon radiation associated to 2 −> 2 hard parton scattering. It has been noticed that the Q-matrix associated to gg −> gg has a surprising symmetry (relating external and internal degrees of freedom). I developed tools to derive the Q-matrices associated to2 −> 2 scatterings involving generalized partons, in order to explore if the symmetry observed for gg −> gg is fortuitous or not.