Understanding Hawking radiation from simple models of atomic Bose-Einstein condensates

This chapter is an introduction to the Bogoliubov theory of dilute Bose condensates as applied to the study of the spontaneous emission of phonons in a stationary condensate flowing at supersonic speeds. This emission process is a condensed-matter analog of Hawking radiation from astrophysical black holes but is derived here from a microscopic quantum theory of the condensate without any use of the analogy with gravitational systems. To facilitate physical understanding of the basic concepts, a simple one-dimensional geometry with a stepwise homogenous flow is considered which allows for a fully analytical treatment.Comment: 41 pages. to appear in the proceedings of the IX SIGRAV School on 'Analogue Gravity', Como (Italy), May 201

Mortality rate and risk factors for gastrointestinal bleeding in elderly patients

Background: Gastrointestinal bleeding (GIB) is burdened by high mortality rate that increases with aging. Elderly patients may be exposed to multiple risk factors for GIB. We aimed at defining the impact of GIB in elderly patients. Methods: Since 2008, samples of elderly patients (age 65 65 years) with multimorbidity admitted to 101 internal medicine wards across Italy have been prospectively enrolled and followed-up (REPOSI registry). Diagnoses of GIB, length of stay (LOS), mortality rate, and possible risk factors, including drugs, index of comorbidity (Cumulative Illness Rating Scale [CIRS]), polypharmacy, and chronic diseases were assessed. Adjusted multivariate logistic regression models were computed. Results: 3872 patients were included (mean age 79 \ub1 7.5 years, F:M ratio 1.1:1). GIB was reported in 120 patients (mean age 79.6 \ub1 7.3 years, F:M 0.9:1), with a crude prevalence of 3.1%. Upper GIB occurred in 72 patients (mean age 79.3 \ub1 7.6 years, F:M 0.8:1), lower GIB in 51 patients (mean age 79.4 \ub1 7.1 years, F:M 0.9:1), and both upper/lower GIB in 3 patients. Hemorrhagic gastritis/duodenitis and colonic diverticular disease were the most common causes. The LOS of patients with GIB was 11.7 \ub1 8.1 days, with a 3.3% in-hospital and a 9.4% 3-month mortality rates. Liver cirrhosis (OR 5.64; CI 2.51\u201312.65), non-ASA antiplatelet agents (OR 2.70; CI 1.23\u20135.90), and CIRS index of comorbidity >3 (OR 2.41; CI 1.16\u20134.98) were associated with GIB (p < 0.05). Conclusions: A high index of comorbidity is associated with high odds of GIB in elderly patients. The use of non-ASA antiplatelet agents should be discussed in patients with multimorbidity