Mapping prior information onto LMI eigenvalue-regions for discrete-time subspace identification

In subspace identification, prior information can be used to constrain the eigenvalues of the estimated state-space model by defining corresponding LMI regions. In this paper, first we argue on what kind of practical information can be extracted from historical data or step-response experiments to possibly improve the dynamical properties of the corresponding model and, also, on how to mitigate the effect of the uncertainty on such information. For instance, prior knowledge regarding the overshoot, the period between damped oscillations and settling time may be useful to constraint the possible locations of the eigenvalues of the discrete-time model. Then, we show how to map the prior information onto LMI regions and, when the obtaining regions are non-convex, to obtain convex approximations.Comment: Under revie

Tailoring exchange interactions in engineered nanostructures: Ab initio study

We present a novel approach to spin manipulation in atomic-scale nanostructures. Our ab initio calculations clearly demonstrate that it is possible to tune magnetic properties of sub-nanometer structures by adjusting the geometry of the system. By the example of two surface-based systems we demonstrate that (i) the magnetic moment of a single adatom coupled to a buried magnetic Co layer can be stabilized in either a ferromagnetic or an antiferromagnetic configuration depending on the spacer thickness. It is found that a buried Co layer has a profound effect on the exchange interaction between two magnetic impurities on the surface. (ii) The exchange interaction between magnetic adatoms can be manipulated by introducing artificial nonmagnetic Cu chains to link them.Comment: 4 pages, submitted to PR

Tracking ancient beach-lines inland: 2600-year-old dentate-stamped ceramics at Hopo, Vailala River region, Papua New Guinea

The Lapita expansion took Austronesian seafaring peoples with distinctive pottery eastward from the Bismarck Archipelago to western Polynesia during the late second millennium BC, marking the first stage in the settlement of Oceania. Here it is shown that a parallel process also carried Lapita pottery and people many hundreds of kilometres westward along the southern shore of Papua New Guinea. The key site is Hopo, now 4.5km inland owing to the progradation of coastal sand dunes, but originally on the sea edge. Pottery and radiocarbon dates indicate Lapita settlement in this location c.600 BC, and suggest that the long-distance maritime networks linking the entire southern coast of Papua New Guinea in historical times may trace their origin to this period