Beiträge zur Kenntniss der Albumosen

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On the Stability of Damped Timoshenko Systems: Cattaneo Versus Fourier Law

We consider hyperbolic Timoshenko-type vibrating systems that are coupled to a heat equation modeling an expectedly dissipative effect through heat conduction. While exponential stability under the Fourier law of heat conduction holds, it turns out that the coupling via the Cattaneo law does not yield an exponentially stable system. This seems to be the first example that a removal of the paradox of infinite propagation speed inherent in Fourier’s law by changing to the Cattaneo law causes a loss of the exponential stability property. Actually, for systems with history, the Fourier law keeps the exponential stability known for the pure Timoshenko system without heat conduction, but introducing the Cattaneo coupling even destroys this property. This work was supported by the DFG-project “Hyperbolic Thermoelasticity” (RA 504/3-1).     

Worst-case performance of Wong's Steiner tree heuristic

A study of the worst-case performance of Wong's heuristic for the Steiner problem in directed networks (SPDN) is presented in this paper.SPDN is a classic combinatorial optimization problem having the status of a very difficult problem (NP-hard problem) and it is known as an optimization model for a broad class of problems in networks. Several exact and heuristic approaches have been designed for SPDN in the last twenty five years.Some papers analyze theoretical and experimental behavior of heuristics for SPDN, specially for undirected networks, but none of these has studied the worst-case performance of Wong's heuristic. In this paper, we find a lower bound for that performance and show that this bound is consistent with comparable results in the literature on SPDN and its undirected version.     

Additive und stetige Funktionaloperationen

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Zur Bestimmung des spezifischen Gewichtes des Wachses

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