Clustering and the hyperbolic geometry of complex networks

Clustering is a fundamental property of complex networks and it is the mathematical expression of a ubiquitous phenomenon that arises in various types of self-organized networks such as biological networks, computer networks or social networks. In this paper, we consider what is called the global clustering coefficient of random graphs on the hyperbolic plane. This model of random graphs was proposed recently by Krioukov et al. as a mathematical model of complex networks, under the fundamental assumption that hyperbolic geometry underlies the structure of these networks. We give a rigorous analysis of clustering and characterize the global clustering coefficient in terms of the parameters of the model. We show how the global clustering coefficient can be tuned by these parameters and we give an explicit formula for this function.Comment: 51 pages, 1 figur

Durchimpfung von Kleinkindern im Kanton Zürich

At present there is a shortage of data regarding the rate of routine immunization in Swiss children. To address this deficit, a representative cross sectional study was conducted in the Canton of Zurich with 210 children aged between 24 and 36 months. Data was taken from the individual official vaccination certificates. 178 vaccination certificates (55.1% female and 44.9% male) were evaluated, corresponding to a response rate of 84.8%. With children of foreign nationalities, the response rate was 66.7%, whereas the response rate of Swiss children was 90.6% (p < 0.001). The response rate of children of a European nationality outside the European Union was especially poor (33.3%). The immunization rate with three doses of diphtheria, tetanus and poliomyelitis vaccines was 99.4%, and that of the pertussis vaccine was 93.3%. With the vaccines for measles, mumps and rubella the rates were 80.3%, 78.1% and 77.5% respectively. Vaccination rate against Haemophilus influenzae type B was 74.7% with two doses, and 61.2% with three doses. The timing and the number of doses of the vaccines used for infants in the Canton of Zurich were satisfactory. However, the vaccination rate for measles, mumps and rubella is inadequate. Attention should be paid to this problem and also to possible insufficient care of foreign children

Khat chewing is a risk factor for acute myocardial infarction: a case-control study

Aim Khat chewing is a common habit in Yemen and east African countries. Millions of people chew khat leaves daily for its euphoric and energetic effects and to increase alertness. Cathinone, the main active substance in fresh khat leaves, has sympathomimetic effects which increase heart rate and blood pressure. The aim was to examine the hypothesis that khat chewing is a risk factor for acute myocardial infarction (AMI) using a hospital-based matched case-control study. Method Between 1997 and 1999, we selected 100 patients admitted to the Al-Thawra teaching hospital Sana’a ICU, Yemen with acute myocardial infarction. 100 control subjects, matched to cases for sex and age, were recruited from the outpatients clinics of the same hospital. A questionnaire was completed for case and control groups covering personal history of khat chewing, smoking, hypertension, diabetes and any family history of myocardial infarction. A blood sample was collected for performing lipid profiles. Cases and controls were compared by analysis conducted using conditional logistic regression which corrected for baseline imbalances leading to less biased estimations of odds ratio (OR). The risk associated with each classical factor and khat chewing habits was then investigated. OR values greater than 2.5 indicated a significant risk factor. Results Khat chewing was significantly higher among the AMI case group than control group (OR = 5.0, 95% CI 1.9–13.1). A dose–response relationship was observed, the heavy khat chewers having a 39-fold increased risk of AMI. Conclusion This study indicates that khat chewing is associated with AMI and is an independent dose-related risk factor for the development of myocardial infarction