5,047 research outputs found
Rate-dependent and antiarrhythmic reentrant tachycardia (AVNRT) effects of simvastatin in isolated rabbit atrioventricular nodal model
Background and purpose: Several previous studies have shown the direct and indirect effects of statins on supraventricular and ventricular arrhythmia. The purpose of the present study is to determine (1) whether Simvastatin modifies the rate-dependent properties of the AV node, (2) to what extent such changes are related to effect of Simvastatin on the basic properties of AV nodal conduction and refractoriness. Materials and methods: AV nodal refractoriness (AVERP & AVFRP) and rate dependency protocols Fatigue and Facilitation were used to assesse the electrophysiological properties of AV node. We used an isolated perfussed rabbit with AV nodal preparation in one group (N=8). The stimulation protocols were carried out during control phase and in the presence of various concentrations of Simvastatin (0.5 , 0.8 , 1, 3 ,10 μm). Results: Simvastatin in concentration-dependent manner successfully prolonged effective and functional nodal refractory period (AVERP & AVFRP). Also an increase in Wenckebach cycle length was observed. Simvastatin in high concentration (3,10 μm) increases the arrhythmia threshold. Various concentrations of simvastatin increased fatigue, but it reached to significant level only at 30 μM. Conclusion: Simvastatin has potential anti-AVNRT effects by elevating arrhythmia threshold and prolongation of nodal refractoriness
Clustering by soft-constraint affinity propagation: Applications to gene-expression data
Motivation: Similarity-measure based clustering is a crucial problem
appearing throughout scientific data analysis. Recently, a powerful new
algorithm called Affinity Propagation (AP) based on message-passing techniques
was proposed by Frey and Dueck \cite{Frey07}. In AP, each cluster is identified
by a common exemplar all other data points of the same cluster refer to, and
exemplars have to refer to themselves. Albeit its proved power, AP in its
present form suffers from a number of drawbacks. The hard constraint of having
exactly one exemplar per cluster restricts AP to classes of regularly shaped
clusters, and leads to suboptimal performance, {\it e.g.}, in analyzing gene
expression data. Results: This limitation can be overcome by relaxing the AP
hard constraints. A new parameter controls the importance of the constraints
compared to the aim of maximizing the overall similarity, and allows to
interpolate between the simple case where each data point selects its closest
neighbor as an exemplar and the original AP. The resulting soft-constraint
affinity propagation (SCAP) becomes more informative, accurate and leads to
more stable clustering. Even though a new {\it a priori} free-parameter is
introduced, the overall dependence of the algorithm on external tuning is
reduced, as robustness is increased and an optimal strategy for parameter
selection emerges more naturally. SCAP is tested on biological benchmark data,
including in particular microarray data related to various cancer types. We
show that the algorithm efficiently unveils the hierarchical cluster structure
present in the data sets. Further on, it allows to extract sparse gene
expression signatures for each cluster.Comment: 11 pages, supplementary material:
http://isiosf.isi.it/~weigt/scap_supplement.pd
Involutive Bases Algorithm Incorporating F5 Criterion
Faugere's F5 algorithm is the fastest known algorithm to compute Groebner
bases. It has a signature-based and an incremental structure that allow to
apply the F5 criterion for deletion of unnecessary reductions. In this paper,
we present an involutive completion algorithm which outputs a minimal
involutive basis. Our completion algorithm has a nonincremental structure and
in addition to the involutive form of Buchberger's criteria it applies the F5
criterion whenever this criterion is applicable in the course of completion to
involution. In doing so, we use the G2V form of the F5 criterion developed by
Gao, Guan and Volny IV. To compare the proposed algorithm, via a set of
benchmarks, with the Gerdt-Blinkov involutive algorithm (which does not apply
the F5 criterion) we use implementations of both algorithms done on the same
platform in Maple.Comment: 24 pages, 2 figure
Stress among medical students of Gorgan (South East of Caspian Sea), Iran
Objective: This study aims to estimate the prevalence of psychological stress and association between the levels of stress and study variables among Gorgan medical students. Materials and methods: All three year medical students (129 basic sciences students) in Gorgan Faculty of Medicine, Golestan University of medical Sciences, were asked to complete the Kessler 10 questionnaire. Results: The findings showed mild, moderate and severe stress among 26.22%, 20.50% and 14.75% study subjects. 39.35% of medical students had no stress. There was statistically significant association between year of study and stress levels (p= 0.040). Conclusion: The results indicate that there is a decrease in the psychological health of first year medical students. Provided that stress management courses are organised by medical schools, when the students arrive, they will cope up with the stress in coming years. These courses may reduce the negative effects of stress on medical students. By providing such courses and reducing stress level, medical students may improve their medical education
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