Carbon dioxide and water incorporation mechanisms in SrFeO3-δ phases: a computational study.

With a higher propensity for low temperature synthesis routes along with a move toward lower solid oxide fuel cell operating temperatures, water and carbon dioxide incorporation in strontium ferrite is of importance. Despite this, the mechanisms are not well understood. In this work, classical-potential-based computational techniques are used to determine the favourability of water and CO2 incorporation mechanisms in both SrFeO3-δ and SrFeO2.5. Our studies suggest that intrinsic Frenkel and Schottky type defects are unlikely to form, but that water and carbon dioxide incorporation are favourable in both phases. Water incorporation is likely for both the cubic and brownmillerite phases, with hydroxyl ions preferring to sit on octahedral oxygen sites in both structures, causing slight tilting of the shared octahedra. Interstitial hydroxyl ions are only likely for the brownmillerite phase, where the hydroxyl ions are most stable between adjacent FeO4 tetrahedral chains. Carbon dioxide incorporation via carbonate defects is most favourable when a carbonate molecule exists on an iron site, preferring the iron site with lower oxygen coordination. This involves formation of multiple oxygen vacancies surrounding the iron site, and thus we conclude that carbonate can trap oxygen vacancies.

Endoscopic cecal perforation: mechanisms of injury.

OBJECTIVE: Most endoscopic perforations of the colon occur in the rectosigmoid area and are thought to be secondary to direct injury from the endoscopic instrument. The aim of this study was to describe the mechanisms of injury and clinical outcome of endoscopic perforation involving the cecum. METHODS: Retrospective review of 6684 consecutive colonoscopic procedures performed at a university hospital over a 7-yr period. RESULTS: Colonoscopy was complicated by perforation in 0.22%. Five of the 15 perforations occurred in the cecum. The mean age of these five patients was 79.6 +/- 17.7 yr (mean +/- SD). Indications for the procedure were bleeding (n = 4) and suspected obstructing cecal mass (n = 1). Abnormal endoscopic findings included diverticulosis, vascular malformations, cecal ulcer/inflammation, mass, and polyps. Perforation was directly attributable to an ancillary procedure (three routine biopsies, one electrocautery) in the cecal area in four patients, and cecal pathology (inflammation, ulceration) was a contributing risk factor in three patients. Mortality was 80%. In contrast, a noncecal perforation usually occurred at the sigmoid region and was associated with technical difficulties, e.g., inability to traverse a stricture or reach the cecum. CONCLUSIONS: Routine forceps biopsy (without electrocautery) is an under-recognized cause of cecal perforation. Ancillary endoscopic interventions in the cecal region should be minimized in elderly patients with evidence of cecal inflammation. Pneumatic injury may be an additional risk factor for cecal perforation in patients with a colonic stricture or a tortuous colon.

Odynophagia caused by a pericardial diverticulum.

A 31-yr-old female presented with odynophagia and weight loss. Upper gastrointestinal endoscopy, esophageal manometry, and chest x-ray all were normal. However, computerized tomography of the chest revealed a mediastinal mass, which on mediastinoscopy proved to be a pericardial diverticulum. Surgical excision of this diverticulum resulted in complete resolution of her symptoms. This case report illustrates that mediastinal lesions should be considered as a potential cause of odynophagia when esophageal disease has been ruled out.

Teaching dressing skills to a severely retarded child.

An eight-year-old, severely retarded boy was taught to remove his polo shirt independently in sixteen training sessions using operant techniques. Reinforcement was dispensed contingent upon successful independent performance on each of five undressing subtasks.