Eckhard Steffen

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Bacterial translocation is defined as the passage of indigenous bacteria from the gastrointestinal (GI) tract through the lamina propria to the mesenteric lymph nodes (MLN) and other organs. We compared the relative abilities of various aerobic, facultatively anaerobic, and obligately anaerobic bacteria to translocate from the GI tract to the MLN in(More)
Snarks are cubic graphs with chromatic index 0 = 4. A snark G is called critical if 0 (G?fv; wg) = 3 for any two adjacent vertices v and w, and it is called bicritical if 0 (G ? fv; wg) = 3 for any two vertices v and w. We construct innnite families of critical snarks which are not bicritical. This solves a problem stated by Nedela and Skoviera in 7].
We develop four constructions for nowhere-zero 5-ows of 3-regular graphs which satisfy special structural conditions. Using these constructions we show a minimal counterexample to Tutte's 5-ow conjecture is of order 44 and therefore every bridgeless graph of nonorientable genus 5 has a nowhere-zero 5-ow. One of the structural properties is formulated in(More)
We show that there is exactly one 3-critical graph of order 22 and that there are exactly nine of order 24. The graph of order 22 is shown to be the smallest 3-critical graph of even order. We also show that there are exactly two 4-critical graphs of order 18, and that these graphs are the smallest 4-critical graphs of even order. The results are obtained(More)