Casimir force in dense confined electrolytes

Understanding the force between charged surfaces immersed in an electrolyte solution is a classic problem in soft matter and liquid-state theory. Recent experiments showed that the force decays exponentially but the characteristic decay length in a concentrated electrolyte is significantly larger than what liquid-state theories predict based on analysing correlation functions in the bulk electrolyte. Inspired by the classical Casimir effect, we consider an alternative mechanism for force generation, namely the confinement of density fluctuations in the electrolyte by the walls. We show analytically within the random phase approximation, which assumes the ions to be point charges, that this fluctuation-induced force is attractive and also decays exponentially, albeit with a decay length that is half of the bulk correlation length. These predictions change dramatically when excluded volume effects are accounted for within the mean spherical approximation. At high ion concentrations the Casimir force is found to be exponentially damped oscillatory as a function of the distance between the confining surfaces. Our analysis does not resolve the riddle of the anomalously long screening length observed in experiments, but suggests that the Casimir force due to mode restriction in density fluctuations could be an hitherto under-appreciated source of surface-surface interaction

Development of adenocarcinoma in chronic fistula in Crohn's disease

The authors report the case of a 55 yr-old woman suffering from Crohn's disease since 31 years with stricture and fistulas developed in the ileocolic junction and anorectal portion. Long-standing anorectal fistulas and stricture led to adenocarcinoma and finally fistulisation in the vagina. Diagnosis was made by perineal examination with biopsies under general anaesthesia. Treatment was first posterior pelvectomy with resection of the anterior wall of vagina. Secondarily, radiochemotherapy was administrated. The authors discuss the incidence and risk factors of carcinoma in Crohn's disease with chronic fistulas