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Winfried Just 《Journal of Mathematical Analysis and Applications》2008,348(2):620-636
It is demonstrated that a Kolmogorov-type competition model featuring species allocation and gain functions can possess multiple coexistence states. Two examples are constructed: one in which the two competing species possess rectangular allocation functions but distinct gain functions, and the other in which one species has a rectangular allocation function, the second species has a bi-rectangular allocation function, and the two species share a common gain function. In both examples, it is shown that the species nullclines may intersect multiple times within the interior of the first quadrant, thus creating both locally stable and unstable equilibrium points. These results have important applications in the study of plant competition for sunlight, in which the allocation functions describe the vertical placement of leaves for two competing species, and the gain functions represent rates of photosynthesis performed by leaves at different heights when shaded by overlying leaves belonging to either species. 相似文献
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Continuous electrochemical sensing is often carried out in order to track the growth of cells as an alternative to optical monitoring. Planar sensors and multi-sensor chips are applied in case of adhered growing cells, and usually introduced into lab-on-chip systems. Repeated recalibration is necessary with most chemosensors so far and this limits the operational lifetime of such lab-on-chip systems to a few days. An assembly is presented here that eliminates this disadvantage and enables the monitoring of a long-term cultivation of tissue. Cell cultures and sensor are arranged such that they can be separated or contacted at variable times without having an impact on the growth of the cells. The use of a biocompatible nano-porous membrane is especially important. A multi-well system is described where each well is supplied with a planar multi-sensor chip below the adhered cells to determine (a) pH, (b) glucose, (c) oxygen, and—optionally—impedance, for example during the cultivation of cartilage tissue. 相似文献
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Hans Postma Luc Amkreutz Alessandro Borella Martijn Clarijs Hans Kamermans Winfried Kockelmann Anna Paradowska Peter Schillebeeckx Dirk Visser 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(3):641-652
Two neutron based techniques, neutron resonance capture analysis (NRCA) and time-of-flight neutron-diffraction (TOF-ND) have
been used to determine the elemental composition and structure of a precious and very well preserved all-metal sword from
the Bronze Age. This Buggenum sword was on loan from the National Museum of Antiquities (NMA) in Leiden (NL). NRCA and TOF-ND
experiments have been carried out at a number of more or less identical positions of the sword. The tin-bronze ratio and the
relative amounts of some minor elements (Sb, As, Ag, In) have been determined. The results of neutron diffraction measurements
showed considerable tin-segregation, and clear indications of hardening on the edges of the blade. In addition, radiographs
using Bremsstrahlung revealed the construction of the hilt–blade connection. The work was carried out at the EC Joint Research
Centre IRMM in Geel (B) and at the ISIS facility of the Rutherford Appleton Laboratory (UK). 相似文献
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Néel N Berndt R Kröger J Wehling TO Lichtenstein AI Katsnelson MI 《Physical review letters》2011,107(10):106804
Linear CoCu(n)Co clusters on Cu(111) fabricated by atomic manipulation represent a two-site Kondo system with tunable interaction. Scanning tunneling spectroscopy reveals oscillations of the Kondo temperature T(K) with the number n of Cu atoms for n≥3. Density functional calculations show that the Ruderman-Kittel-Kasuya-Yosida interaction mediated by the Cu chains causes the oscillations. Calculations find ferromagnetic and antiferromagnetic interaction for n=1 and 2, respectively. Both interactions lead to a decrease of T(K) as experimentally observed. 相似文献