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The existence of Steiner triple systems STS(n) of order n containing no nontrivial subsystem is well known for every admissible n. We generalize this result in two ways. First we define the expander property of 3-uniform hypergraphs and show the existence of Steiner triple systems which are almost perfect expanders. Next we define the strong and weak spreading property of linear hypergraphs, and determine the minimum size of a linear triple system with these properties, up to a small constant factor. A linear triple system on a vertex set V has the spreading, or respectively weakly spreading property if any sufficiently large subset V 0 ⊂ V contains a pair of vertices with which a vertex of V rV 0 forms a triple of the system. Here the condition on V 0 refers to jV 0j 4 or V 0 is the support of more than one triples, respectively. This property is strongly connected to the connectivity of the structure the so-called inuence maximisation. We also discuss how the results are related to Erd}os' conjecture on locally sparse STSs, subsquare-free Latin-squares and possible applications in finite geometry. [ABSTRACT FROM AUTHOR]

Caves offer bats refuges for hibernation, breeding and other social events. Their quality is important for species distribution. The role of cave microclimate as well as other environmental factors influencing the distribution of cave-dwelling species, is poorly known. We tested the significance of cave variables (length, temperature, elevation, occurrence of water) and geographical location for the presence of bats during hibernation and the breeding season in five regions in Romania. To detect species' environmental relationships, we used canonical correspondence analyses for winter bat aggregations and principal components analysis for maternity colonies. We analysed the factors influencing the distribution of bats by using two sets of explanatory variables reflecting cave characteristics and geographical locations. Winter aggregation was divided into three groups: (1) bat species that prefer high temperatures ( Rhinolophus euryale, Myotis cappacinii) and hibernate at a low altitude; (2) species ranging from mid- to high elevation and low temperature (Myotis myotis/oxygnathus group); (3) species that hibernate in large, cold cave systems with a constant flow of the water (Pipistrellus pipistrellus, Nyctalus noctula, Barbastella barbastellus). Maternity colonies were divided into those that select either high (rhinolophids) or low temperatures (My. myotis/oxygnathus and Miniopterus schreibersii). The most important factors influencing the distribution of bats are the temperature in caves and their geographical location. This information was combined with IUCN's Red List data as well as with the number of individuals occurring in caves with the aim of identifying the key sites for conservation. The majority of these sites, which also constitute the refuges for vulnerable species, are located in west and south-western Romania. Seven caves provide shelter throughout the year for 122 000 individuals of 14 species. [ABSTRACT FROM AUTHOR]

We present five years' experience with mitral plication annuloplasty, performed with a semicircular buttressed suture around the posterior leaflet in 130 patients (mean age 58 +/- 11 years) with primary mitral valve disease (n = 71) or functional mitral regurgitation (n = 59). In 65 cases the mitral valve itself was also repaired. Concomitant myocardial revascularization was performed in 40 cases and aortic valve replacement in 43. All but three patients were followed up (97.6%). Postoperative echocardiography showed acceptable mitral area (2.28 +/- 0.39 cm2) and good valve competence in all cases. Inhospital mortality was 3% and late mortality 4.8%. During the follow-up period (22.8 +/- 10.9 months) 8 patients (6.6%) required mitral valve replacement because of progression of native valve disease (n = 4), technical failure (2) or expansion of the annuloplasty suture (2). Mitral annuloplasty thus can be performed simply and with good results, using a strong, non-stretchable buttressed suture. This procedure can be an inexpensive alternative to ring implantation. [ABSTRACT FROM AUTHOR]

Objective: The hydrodynamic parameters and leaflet motion of the porcine pulmonary root and valve and the performance of the pulmonary autograft implanted in subcoronary position or as a free-standing root were investigated at systemic and pulmonary pressures in vitro., Methods: Ten fresh pulmonary and aortic roots (anulus diameter, 20-25 mm) were tested in a pulsatile flow simulator. Five free-sewn pulmonary valves were implanted in aortic roots in the subcoronary position, and 5 pulmonary roots were implanted as free-standing roots. The external diameter of the roots was measured at the sinotubular junction in a pressure range of 0 to 120 mm Hg. The transvalvular gradient and regurgitation were measured, and the effective orifice area was calculated. The leaflet motion was recorded on video tape., Results: The fresh pulmonary roots were more compliant than their aortic counterparts (33% +/- 3. 0% vs 7% +/- 1.5% with dilatation at 0-30 mm Hg and 46% +/- 8.4% vs 35% +/- 7.8% with dilatation at 0-120 mm Hg). The pulmonary roots had a lower pressure drop at systemic than at pulmonary pressures. The pressure drops of the pulmonary roots were also lower than those of the aortic roots in the systemic pressure range. The leaflet opening of the pulmonary valve was triangular, with low bending deformation at all pressures. Implanting the free-sewn pulmonary valve in the subcoronary position or the pulmonary root as a free-standing root did not affect the hydrodynamic parameters and leaflet motion adversely., Conclusion: The pulmonary valve and root could easily withstand aortic pressures in vitro. A biphasic dilatation curve ensures that higher pressures did not overdilate the pulmonary root. Moreover, valve performance was better at systemic pressures.

Background: An in vitro model has been established to investigate the effect of sizing on the hydrodynamic characteristics and leaflet motion of the Medtronic Freestyle valve., Methods: The valves were tested in fresh porcine aortic roots. Two or three different sizes of valves were implanted in the same aortic root one after the other. The compliance of the fresh aortic and the composite roots was measured in the pressure range of 0 to 120 mm Hg, and the composite roots were then tested in a pulsatile flow simulator. The transvalvular gradient and degree of regurgitation were measured and the effective orifice area and performance index were calculated. Leaflet motion was recorded on video., Results: The fresh aortic roots dilated by average 39.4% as the hydrostatic pressure rose from 0 to 120 mm Hg. Implantation of the Medtronic Freestyle valve did not change the distensibility of the aortic root significantly. The sizing protocol did not affect significantly the hydrodynamic performance. However, a significantly lower open leaflet bending deformation was found in the undersized valves. Regurgitation was found only at 2-mm undersized valves., Conclusions: Leaflet motion of the Medtronic Freestyle valve in vitro was best if 1 mm undersized, and this may be beneficial to long-term durability.

Objectives: We established an in vitro model to investigate the effects of valve sizing on the hemodynamic characteristics and leaflet motion of the Toronto SPV valve (St Jude Medical, Inc, St Paul, Minn)., Methods: Nine valves were first implanted in fresh porcine aortic roots and then retested in glutaraldehyde-treated porcine aortic roots. Three valves were 1- to 2-mm oversized, 3 were 1- to 2-mm undersized, and there were 3 size-for-size implantations. The elasticities of the aortic roots and the composite roots were measured in the pressure range between 0 and 120 mm Hg, and the composite roots were then tested in a pulsatile flow simulator. The transvalvular gradient and regurgitation were measured and the effective orifice area and performance index were calculated for each root. Leaflet motion was recorded on videotape., Results: The external diameter of the fresh root increased by 35% as the hydrostatic pressure rose from 0 to 120 mm Hg, as compared with 11% for the glutaraldehyde-treated root. Valve implantation in the fresh root reduced the distensibility to 22% but did not change distensibility in the glutaraldehyde-treated root. The effective orifice area was dependent on the valve size, with the transvalvular gradient decreasing as the valve size increased. For the same size of valve the hydrodynamic parameters were slightly better if the valve was undersized by 1 mm. A significant difference in favor of the undersized valves was found in open-leaflet bending deformation., Conclusion: Leaflet motion of the stentless porcine aortic valve in vitro is improved if the valve is slightly undersized, and this may be beneficial to the long-term durability of the prosthesis.