Apical periodontitis is caused primarily by microorganisms residing in the root canals of affected teeth. Nevertheless, there is convincing evidence implicating other independent factors that adversely affect the outcome of conventional root canal therapy. In this paper, morphological evidence is presented in support of the potential role of two endogenous factors that may interfere with post-endodontic healing of the periapex. The specimens consisted of a surgical biopsy of an asymptomatic periapical lesion which persisted for a follow-up period of 44 months. The biopsy was processed for correlated light and electron microscopy. The lesion was characterized by the presence of a large central lumen lined by a stratified squamous epithelium. The most striking feature of the lesion was the presence of vast numbers of cholesterol crystals which congregated in the connective tissue surrounding the cyst cavity. Extensive light and electron microscopic investigation of the apical part of the root canal and the lesion failed to reveal the presence of microorganisms. These findings strongly suggest that intrinsic factors like the accumulation of certain tissue break-down products such as cholesterol crystals, and the cystic condition of the lesion itself, can adversely affect the healing process of the periapex following root canal therapy. Consequently, such apical lesions can remain refractory to conventional endodontic therapy for long periods of time.

No abstract

In supersonic nozzle beams of sodium, potassium, and Na/K molecular aggregates Mx have been investigated by several techniques based on mass spectrometry. By electron impact ionization with energy of 20 eV clusters with x≳4 are not observable. Photoionization near the threshold allows identification of Naxx?16, Kxx?12, and NaxKyx+y?6. Single photon ionization thresholds for Naxx?14 are given, this being the hitherto longest contiguous series of any property as a function of cluster size. For Kxx?8 and for 8 Na/K mixed clusters PI thresholds are similarly determined. Very accurate two photon photoionization thresholds for Na2 and K2 have been obtained. Theoretical models of metal clusters from recent publications are not able to adequately interpret the electronic properties of these particles as reflected by the ionization potentials.

Интервью с Джоном Наем: «Всех нас интересовала область применения экономического подхода к общим проблемам социальных наук» (перевод А. А. Куракина

Mixed metal clusters of sodium and cesium with gold have been generated in a supersonic expansion from the mixed vapor phase. Their tendency towards binary cluster formation, relative thermodynamic stability, and ionization potentials have been experimentally and computationally investigated. The properties of the NaxAu clusters may be understood within an electronic shell model based on delocalized cluster orbitals, whereas the characteristics of CsxAu are indicative of substantial ionic interactions. Relativistic density functional calculations have been performed to elucidate the cluster electronic structure and to rationalize observed properties which may not be accounted for by the jellium model. The properties of these finite-size clusters are shown to be related to the known bulk intermetallic compounds sodium–gold and cesium–gold (cesium aurid), respectively.