2D quantum gravity from quantum entanglement.

In quantum systems with many degrees of freedom the replica method is a useful tool to study the entanglement of arbitrary spatial regions. We apply it in a way that allows them to backreact. As a consequence, they become dynamical subsystems whose position, form, and extension are determined by their interaction with the whole system. We analyze, in particular, quantum spin chains described at criticality by a conformal field theory. Its coupling to the Gibbs' ensemble of all possible subsystems is relevant and drives the system into a new fixed point which is argued to be that of the 2D quantum gravity coupled to this system. Numerical experiments on the critical Ising model show that the new critical exponents agree with those predicted by the formula of Knizhnik, Polyakov, and Zamolodchikov.

Width of the confining string in Yang-Mills theory.

We investigate the transverse fluctuations of the confining string connecting two static quarks in (2+1)D SU(2) Yang-Mills theory using Monte Carlo calculations. The exponentially suppressed signal is extracted from the large noise by a very efficient multilevel algorithm. The resulting width of the string increases logarithmically with the distance between the static quark charges. Corrections at intermediate distances due to universal higher-order terms in the effective string action are calculated analytically. They accurately fit the numerical data.

Predicting mortality of patients hospitalized for acutely exacerbated chronic obstructive pulmonary disease.

PURPOSE: To identify factors affecting the short-term prognosis of patients with acutely exacerbated chronic obstructive pulmonary disease (COPD). PATIENTS AND METHODS: The 590 patients having COPD as primary disease who were hospitalized in the pneumology unit of a university hospital from 1981 to 1990 were studied. A standardized protocol for the treatment of acutely exacerbated COPD was adopted for all the patients. The patient records were retrospectively analyzed by two observers, and 23 clinical and laboratory variables defining the patient status on admission were collected. Age and arterial gas data were also taken into account, and the outcome mortality was recorded. Interobserver reproducibility was tested by computing the kappa coefficient and Spearman's rho for dichotomous and continuous variables, respectively. The relationship of clinical and laboratory factors to the outcome was assessed first by univariate analysis and then by a logistic regression analysis assessing the independent predictive role of variables previously shown to be univariately correlated with mortality. RESULTS: The mortality rate was 14.4%. The logistic regression analysis identified four independent predictors of death: age (odds ratio [OR] 1.07; 95% confidence interval [CI] 1.04 to 1.11), alveolar-arterial oxygen gradient greater than 41 mm Hg (OR 2.33; 95% CI 1.39 to 3.90), ventricular arrhythmias (OR 1.91; 95% CI 1.10 to 3.31), and atrial fibrillation (OR 2.27; 95% CI 1.14 to 4.51). CONCLUSIONS: Patients with acutely exacerbated COPD having a high risk of death can be identified at the time of admission. Variables reflecting heart dysfunction are important determinants of this risk. Among pulmonary function data, only alveolar-arterial oxygen gradient contributes to the predictive model.

The cardiopulmonary response to incremental exercise test: the effect of aging.

The aims of the present study were to define the respective roles of the cardiac and respiratory response to exercise as determinants of the age-related physiological decrease in exercise performance, and to assess the relationship between aging and interindividual variability in the response to effort. We studied 91 normal subjects recruited in three age-groups: Group A (42 children, aged 10 +/- 2 years); Group B (29 young adults, aged 27 +/- 5 years); Group C (20 elderly, aged 74 +/- 9 years). All the subjects underwent an incremental cycle ergometer exercise test with a work load increase of 15 W every 2 minutes in groups A and C, and 25 W every 2 minutes in group B, until they achieved 80% of the predicted maximal heart rate. Ventilatory equivalent changes during exercise were significantly lower in group A than in the other two groups, and in group B compared to group C. Exercise-induced changes in oxygen pulse were significantly higher in group A, but no difference was found between groups B and C. Thus, gas-exchange function and overall exercise performance decrease with advancing age, whereas cardiovascular performance is well maintained in normal elderly subjects. Discriminant analysis showed that the exercise response conformed to the group-specific model in 74% and 79% of subjects in groups A and B, but only in 50% of the group C subjects; 5% and 45% of the elderly subjects were functionally classified in groups A and B, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)