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

Infrared spectroscopy of solid normal hydrogen doped with CH₃F and O₂ at 4.2 K: CH₃F:O₂ complex and CH₃F migration

Double doping of solid normal hydrogen with CH₃F and O₂ at about 4.2 K gives evidence of (ortho-H₂)n:CH₃F clusters and of O₂:CH₃F complex formation. A FTIR analysis of the time evolution of the spectra, in the ν₃ C–F stretching mode region, points out a behavior of the clusters very different from that of (ortho-H₂)n:H₂O clusters. The main point is the observation of CH₃F molecules migration in solid para-H₂ at 4.2 K, which is a behavior different from H₂O in identical experimental conditions. This is proved by the increase with time of the CH₃F:O₂ complex integrated intensity with a rate constant K=2.7(2) ⋅10⁻⁴s⁻¹