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

Low energy electron impact on gas phase DNA bases : excitation and negative ions

International audienc

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+)