Dissociative electron attachment to carbon dioxide via the 8.2 eV Feshbach resonance

Momentum imaging experiments on dissociative electron attachment (DEA) to CO{sub 2} are combined with the results of ab initio calculations to provide a detailed and consistent picture of the dissociation dynamics through the 8.2 eV resonance, which is the major channel for DEA in CO{sub 2}. The present study resolves several puzzling misconceptions about this system

Fragmentation processes of ionized 5-fluorouracil in the gas phase and within clusters

We have measured mass spectra for positive ions produced from neutral 5-fluorouracil by electron impact at energies from 0 to 100 eV. Fragment ion appearance energies of this (radio-)chemotherapy agent have been determined for the first time and we have identified several new fragment ions of low abundance. The main fragmentations are similar to uracil, involving HNCO loss and subsequent HCN loss, CO loss, or FCCO loss. The features adjacent to these prominent peaks in the mass spectra are attributed to tautomerization preceding the fragmentation and/or the loss of one or two additional hydrogen atoms. A few fragmentions are distinct for 5-fluorouracil compared to uracil, most notably the production of the reactive moiety CF+. Finally, multiphoton ionization mass spectra are compared for 5-fluorouracil from a laser thermal desorption source and from a supersonic expansion source. The detection of a new fragment ion at 114 u in the supersonic expansion experiments provides the first evidence for a clustering effect on the radiation response of 5-fluorouracil. By analogy with previous experiments and calculations on protonated uracil, this is assigned to NH3 loss from protonated 5-fluorouracil

ICAR: endoscopic skull‐base surgery

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Computational Homogenization of Architectured Materials

Architectured materials involve geometrically engineered distributions of microstructural phases at a scale comparable to the scale of the component, thus calling for new models in order to determine the effective properties of materials. The present chapter aims at providing such models, in the case of mechanical properties. As a matter of fact, one engineering challenge is to predict the effective properties of such materials; computational homogenization using finite element analysis is a powerful tool to do so. Homogenized behavior of architectured materials can thus be used in large structural computations, hence enabling the dissemination of architectured materials in the industry. Furthermore, computational homogenization is the basis for computational topology optimization which will give rise to the next generation of architectured materials. This chapter covers the computational homogenization of periodic architectured materials in elasticity and plasticity, as well as the homogenization and representativity of random architectured materials

MÉCANISMES D'IONISATION SIMPLE ET MULTIPLE DANS QUELQUES VAPEURS MÉTALLIQUES, PAR IMPACT ÉLECTRONIQUE

On montre que de nombreux changements de pente observés dans les courbes d'ionisation des ions atomiques multichargés sont attribuables à l'effet Auger simple (Sr2+, Ba2+, Mn2+, Mn4+). Cependant, dans le cas d'ions très chargés (Mn5+, Mn6+, Cd5+, Cd6+ et quelques ions de In et de Ag) des éjections supplémentaires se produisent, soit pendant l'acte primaire d'ionisation (ionisation primaire multiple : Cd5+, In5+, Ag5+) soit pendant la cascade Auger (transition Auger, multiple In7+, Ag+7).We show that various breaks observed in ionization efficiency curves of multicharged dtomic ions are due to simple Auger process (Sr2+, Ba2+, Mn2+, Mn4+). However in the case of high charged ions (Mn5+, Mn6+, Cd5+, Cd5+ and some Ag and In ions), additional electrons are ejected either during the primary ionization (multiple primary ionization : Cd5+, In5+, Ag5+) or during the Auger cascade (multiple Auger transition In7+, Ag7+)

Ionisation multiple et transitions Auger dans l'indium et l'argent par impact électronique

Relative electron impact cross section of multiply charged ions have been measured for indium and silver up to Ag7+ and In8+. Our results for the value of the ratio Ag2+/Ag+ at E = 75 and 1 000 eV agree very well with the results of Crawford and al. Multiply charged ions with n ≥ 5 are abundantly produced by Auger processes, these being the principal production source for highly charged ions (In 7+, In8+, Ag7+). Mostly, the results show evidence for supplementary electron ejection occuring, either during the primary ionization (In5+, In6+, Ag5+, Ag6+), or during the Auger transition cascade (In7+, Ag7+).Nous avons mesuré les sections efficaces relatives par impact électronique, des ions multiplement chargés de l'argent et de l'indium jusqu'à Ag 7+ et In8+. Les résultats obtenus pour le rapport Ag 2+/Ag+ à E = 75 et 1 000 eV sont en excellent accord avec les valeurs de Crawford et al. Les ions de charge n ≥ 5 sont abondamment formés par des processus Auger, ces derniers étant la source principale de production des ions très chargés (In7+, In8+ , Ag7+). Dans la plupart des cas, les résultats montrent l'évidence d'éjections supplémentaires d'électrons se produisant, soit au cours de l'ionisation primaire (In5+, In6+, Ag 5+, Ag6+), soit au cours de la cascade de transitions Auger (In 7+, Ag7+)