25 research outputs found
Sharp transition towards shared vocabularies in multi-agent systems
What processes can explain how very large populations are able to converge on
the use of a particular word or grammatical construction without global
coordination? Answering this question helps to understand why new language
constructs usually propagate along an S-shaped curve with a rather sudden
transition towards global agreement. It also helps to analyze and design new
technologies that support or orchestrate self-organizing communication systems,
such as recent social tagging systems for the web. The article introduces and
studies a microscopic model of communicating autonomous agents performing
language games without any central control. We show that the system undergoes a
disorder/order transition, going trough a sharp symmetry breaking process to
reach a shared set of conventions. Before the transition, the system builds up
non-trivial scale-invariant correlations, for instance in the distribution of
competing synonyms, which display a Zipf-like law. These correlations make the
system ready for the transition towards shared conventions, which, observed on
the time-scale of collective behaviors, becomes sharper and sharper with system
size. This surprising result not only explains why human language can scale up
to very large populations but also suggests ways to optimize artificial
semiotic dynamics.Comment: 12 pages, 4 figure
Comparison and combination of a hemodynamics/biomarkers-based model with simplified PESI score for prognostic stratification of acute pulmonary embolism: findings from a real world study
Background: Prognostic stratification is of utmost importance for management of acute Pulmonary Embolism (PE) in clinical practice. Many prognostic models have been proposed, but which is the best prognosticator in real life remains unclear. The aim of our study was to compare and combine the predictive values of the hemodynamics/biomarkers based prognostic model proposed by European Society of Cardiology (ESC) in 2008 and simplified PESI score (sPESI).Methods: Data records of 452 patients discharged for acute PE from Internal Medicine wards of Tuscany (Italy) were analysed. The ESC model and sPESI were retrospectively calculated and compared by using Areas under Receiver Operating Characteristics (ROC) Curves (AUCs) and finally the combination of the two models was tested in hemodinamically stable patients. All cause and PE-related in-hospital mortality and fatal or major bleedings were the analyzed endpointsResults: All cause in-hospital mortality was 25% (16.6% PE related) in high risk, 8.7% (4.7%) in intermediate risk and 3.8% (1.2%) in low risk patients according to ESC model. All cause in-hospital mortality was 10.95% (5.75% PE related) in patients with sPESI score ≥1 and 0% (0%) in sPESI score 0. Predictive performance of sPESI was not significantly different compared with 2008 ESC model both for all cause (AUC sPESI 0.711, 95% CI: 0.661-0.758 versus ESC 0.619, 95% CI: 0.567-0.670, difference between AUCs 0.0916, p=0.084) and for PE-related mortality (AUC sPESI 0.764, 95% CI: 0.717-0.808 versus ESC 0.650, 95% CI: 0.598-0.700, difference between AUCs 0.114, p=0.11). Fatal or major bleedings occurred in 4.30% of high risk, 1.60% of intermediate risk and 2.50% of low risk patients according to 2008 ESC model, whereas these occurred in 1.80% of high risk and 1.45% of low risk patients according to sPESI, respectively. Predictive performance for fatal or major bleeding between two models was not significantly different (AUC sPESI 0.658, 95% CI: 0.606-0.707 versus ESC 0.512, 95% CI: 0.459-0.565, difference between AUCs 0.145, p=0.34). In hemodynamically stable patients, the combined endpoint in-hospital PE-related mortality and/or fatal or major bleeding (adverse events) occurred in 0% of patients with low risk ESC model and sPESI score 0, whilst it occurred in 5.5% of patients with low-risk ESC model but sPESI ≥1. In intermediate risk patients according to ESC model, adverse events occurred in 3.6% of patients with sPESI score 0 and 6.65% of patients with sPESI score ≥1.Conclusions: In real world, predictive performance of sPESI and the hemodynamic/biomarkers-based ESC model as prognosticator of in-hospital mortality and bleedings is similar. Combination of sPESI 0 with low risk ESC model may identify patients with very low risk of adverse events and candidate for early hospital discharge or home treatment.
Probabilistic approach to the Bak-Sneppen model
We study here the Bak-Sneppen model, a prototype model for the study of self-organized criticality. In this model several species interact and undergo extinction with a power-law distribution of activity bursts. Species are defined through their “fitness” whose distribution in the system is uniform above a certain threshold. Run time statistics is introduced for the analysis of the dynamics in order to explain the peculiar properties of the model. This approach based on conditional probability theory, takes into account the correlations due to memory effects. In this way, we may compute analytically the value of the fitness threshold with the desired precision. This represents a substantial improvement with respect to the traditional mean field approach
Comparison of endoscopic retrograde cholangiopancreatography between elderly and younger patients for common bile duct stones.
Background. Choledocholithiasis is increasing in elderly subjects.
The introduction of endoscopic retrograde cholangiopancreatography
with biliary sphincterotomy has almost replaced surgery in the treatment
of this condition. The aim of the present study was to evaluate
the rates of successful clearance of common bile duct stones and the
endoscopic techniques used in a population aged 75 years or older
compared with those in a younger age group.
Materials and Methods. A retrospective analysis was made of data
related patients who underwent endoscopic retrograde cholangiopancreatography
for choledocolithiasis in the period 2010-2011. For all
patients, factors such as sex, age at diagnosis, endoscopic treatment
(stone extraction using baskets and balloon, mechanical lithotripsy and
balloon dilatation of the ampulla, placement of a stent or a naso-biliary
tube) and need of surgery were analysed. Two groups of patients were
identified: patients aged <75 years (Group A) and patients aged ≥
Endoscopic papillary balloon dilation for difficult common bile duct stones: Our experience.
AIM: To evaluate the efficacy and safety of endoscopic
balloon dilation (EBD) performed for common bile duct
(CBD) stones.
METHODS: From a computer database, we retrospectively
analyzed the data relating to EBD performed in
patients at the gastrointestinal unit of the Sandro Pertini
Hospital of Rome (small center with low case volume)
who underwent endoscopic retrograde cholangiopancreatography
(ERCP) for CBD from January 1, 2010
to February 29, 2012. All patients had a proven diagnosis
of CBD stones studied with echography, RMNcholangiography
and, when necessary, with computed
tomography of the abdomen (for example, in cases
with pace-makers). Prophylactic therapies, with gabexate
mesilate 24 h before the procedure and with an antibiotic
(ceftriaxone 2 g) 1 h before, were administered
in all patients. The duodenum was intubated with a
side-viewing endoscope under deep sedation with intravenous
midazolam and propofol. The patients were
placed in the supine position in almost all cases