Stefan F. Keller

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Two studies explored the influence of aerobic fitness level on autonomic reactivity to psychosocial stress. Experiment 1 employed a correlational, repeated measures design. A total of 45 men who were physically trained, untrained, or training were tested at three-week intervals over nine weeks. The measure of autonomic reactivity was lability in(More)
As the World Wide Web is growing rapidly, it is getting increasingly challenging to gather representative information about it. Instead of crawling the web exhaustively one has to resort to other techniques like sampling to determine the properties of the web. A uniform random sample of the web would be useful to determine the percentage of web pages in a(More)
Clostridium difficile causes approximately 25% of nosocomial antibiotic-associated diarrheas and most cases of pseudomembranous colitis. We evaluated C. DIFF CHEK, a new screening test that detects glutamate dehydrogenase of C. difficile. Our results showed that this test was comparable to PCR in sensitivity and specificity and outperformed bacterial(More)
This diploma thesis investigated the problem of sampling URLs uniformly at random from the web. Such a method for sampling URLs can be used to estimate various properties of web pages. For example, one could estimate: • The fraction of web pages written in various languages • The coverage of various search engines • The distribution of web pages in(More)
Pharmacological interventions for smoking cessation are typically evaluated using volunteer samples (efficacy trials) but should also be evaluated in population-based trials (effectiveness trials). Nicotine replacement therapy (NRT) alone and in combination with behavioral interventions was evaluated on a population of smokers from a New England Veterans(More)