19 research outputs found
Clustering with minimum spanning trees: How good can it be?
Minimum spanning trees (MSTs) provide a convenient representation of datasets
in numerous pattern recognition activities. Moreover, they are relatively fast
to compute. In this paper, we quantify the extent to which they can be
meaningful in data clustering tasks. By identifying the upper bounds for the
agreement between the best (oracle) algorithm and the expert labels from a
large battery of benchmark data, we discover that MST methods can overall be
very competitive. Next, instead of proposing yet another algorithm that
performs well on a limited set of examples, we review, study, extend, and
generalise existing, the state-of-the-art MST-based partitioning schemes, which
leads to a few new and interesting approaches. It turns out that the Genie
method and the information-theoretic approaches often outperform the non-MST
algorithms such as k-means, Gaussian mixtures, spectral clustering, BIRCH, and
classical hierarchical agglomerative procedures
Hierarchical Clustering with OWA-based Linkages, the Lance-Williams Formula, and Dendrogram Inversions
Agglomerative hierarchical clustering based on Ordered Weighted Averaging
(OWA) operators not only generalises the single, complete, and average
linkages, but also includes intercluster distances based on a few nearest or
farthest neighbours, trimmed and winsorised means of pairwise point
similarities, amongst many others. We explore the relationships between the
famous Lance-Williams update formula and the extended OWA-based linkages with
weights generated via infinite coefficient sequences. Furthermore, we provide
some conditions for the weight generators to guarantee the resulting
dendrograms to be free from unaesthetic inversions
Safety of endoscopic procedures after acute myocardial infarction: A systematic review
Background: The management of patients who develop gastrointestinal (GI) bleeding after
acute myocardial infarction (MI) is difficult due to concerns about possible cardiovascular
complications. Gastroenterologists are often reluctant to perform endoscopic procedures despite
urgent indications. We performed a systematic review of the literature to determine the safety
of endoscopic procedures after MI.
Methods: We searched MEDLINE, EMBASE and the Cochrane Central Register of
Controlled trials for controlled clinical trials or case series examining the diagnostic efficacy
and complications of esophagogastroduodenoscopy (EGD), colonoscopy and flexible sigmoidoscopy
after MI. Title and abstract screening was followed by full-text review with subsequent
data extraction of included studies.
Results: A total of seven studies met inclusion criteria. Four studies evaluated safety and
efficacy of EGD after MI. The reported complication rate ranged between 1-8%, with a large
predominance of minor complications. We found one study addressing safety of flexible
sigmoidoscopy that reported minor complications in two patients. We also identified one study
addressing the safety of colonoscopy after MI, which showed a complication rate of 9%. Most of
these complications were minor. A decision analysis was also included in this review.
Conclusions: Our review demonstrated that endoscopic procedures are safe and beneficial in
stable patients with GI bleeding after recent MI and should be performed without a requisite
delay. Unstable patients should undergo endoscopic procedures only in the intensive care
setting, after stabilization and with close monitoring. (Cardiol J 2012; 19, 5: 447-452
The value of diastolic function parameters in the prediction of left atrial appendage thrombus in patients with nonvalvular atrial fibrillation
BACKGROUND: Left ventricular diastolic impairment and consequently elevated filling pressure may contribute to stasis leading to left atrial appendage thrombus (LAAT) in nonvalvular atrial fibrillation (AF). We investigated whether transthoracic echocardiographic parameters can predict LAAT independent of traditional clinical predictors. METHODS: We conducted a retrospective cohort study of 297 consecutive nonvalvular AF patients who underwent transthoracic echocardiogram followed by a transesophageal echocardiogram within one year. Multivariate logistic regression analysis models were used to determine factors independently associated with LAAT. RESULTS: Nineteen subjects (6.4%) were demonstrated to have LAAT by transesophageal echocardiography. These patients had higher mean CHADS(2) scores [2.6 ± 1.2 vs. 1.9 ± 1.3, P = 0.009], higher E:e’ ratios [16.6 ± 6.1 vs. 12.0 ± 5.4, P = 0.001], and lower mean e’ velocities [6.5 ± 2.1 cm/sec vs. 9.1 ± 3.2 cm/sec, P = 0.001]. Both E:e’ and e’ velocity were associated with LAAT formation independent of the CHADS(2) score, warfarin therapy, left ventricular ejection fraction (LVEF), and left atrial volume index (LAVI) [E:e’ odds-ratio = 1.14 (95% confidence interval = 1.03 – 1.3), P = 0.009; e’ velocity odds-ratio = 0.68 (95% confidence interval = 0.5 – 0.9), P = 0.007]. Similarly, diastolic function parameters were independently associated with spontaneous echo contrast. CONCLUSION: The diastolic function indices E:e’ and e’ velocity are independently associated with LAAT in nonvalvular AF patients and may help identify patients at risk for LAAT
Cohesin Irr1/Scc3 is likely to influence transcription in Saccharomyces cerevisiae via interaction with Mediator complex.
The evolutionarily conserved proteins forming sister chromatid cohesion complex are also involved in the regulation of gene transcription. The participation of SA2p (mammalian ortholog of yeast Irr1p, associated with the core of the complex) in the regulation of transcription is already described. Here we analyzed microarray profiles of gene expression of a Saccharomyces cerevisiae irr1-1/IRR1 heterozygous diploid strain. We report that expression of 33 genes is affected by the presence of the mutated Irr1-1p and identify those genes. This supports the suggested role of Irr1p in the regulation of transcription. We also indicate that Irr1p may interact with elements of transcriptional coactivator Mediator