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GeTe is a narrow-band gap semiconductor, where Ge vacancies generate free charge carriers, holes, forming a self-dopant degenerate system with p-type conductivity, and serves as a base for high-performance multicomponent thermoelectric materials. There is a significant discrepancy between the electronic and thermal transport data for GeTe-based materials reported in the literature, which obscures the baseline knowledge and prevents a clear understanding of the effect of alloying GeTe with various elements. A comprehensive study including XRD, SEM, EDS, Seebeck coefficient, electrical resistivity, thermal conductivity, and 125Te NMR of several GeTe samples was conducted. Similar Seebeck coefficient and electrical resistivity are observed for all GeTe samples used showing that the concentration of Ge vacancies generating charge carriers is constant along the ingot. Very short 125Te NMR spin-relaxation time agrees well with high carrier concentration obtained from the Hall effect measurements. Our data show that at ∼700 K, GeTe has a very large power factor, 42 μWcm-1K-2, much larger than that of any high efficiency thermoelectric telluride at these temperatures. Electronic and thermal properties of GeTe are compared to PbTe, another well-known thermoelectric material, where free charge carriers, holes or electrons, are generated by vacancies on Pb or Te sites, respectively. Discrepancy in the data for GeTe reported in literature can be attributed to the variation in the Ge:Te ratio of solidified samples as well as to different conditions of measurements. [ABSTRACT FROM AUTHOR]

In the design of a residual generator for an unstable plant, the unstable modes are made unobservable from the residual vector. We point out that this cannot be achieved in practice due to the discrepancy between the estimated model and the 'true' plant model. Hence, we deduce that it is not possible to design a residual generator for an unstable plant, unless it is stabilized by an adequate controller. As a by-product, we provide expressions which can be used to quantify the effect of modeling uncertainties on the performance of a residual generator. The factorization approach to control theory is used for the developments.

Colony breeding systems and dispersal strategies of eusocial insects shape the genetic structure at the colony, but also at the population level. Most of the few molecular studies dedicated to termites suggest that winged reproductives disperse far enough to secure the formation of outbred founding pairs. However, these studies almost exclusively focused on wood-feeding termites and knowledge about the dispersal potential of winged reproductives is missing for soil-feeding termites. We investigated the dispersal and mating strategies of Embiratermes neotenicus and Silvestritermes minutus (Termitidae, Syntermitinae), two very abundant soil-feeding species from the Neotropics. In both species, analysis of microsatellite markers indicated low genetic similarity between closely located colonies and low genetic differentiation between populations separated by less than 10 km. Each of the 39 E. neotenicus colonies originated from a single pair of primary reproductives and the mean inbreeding coefficient of sterile castes was only slightly different from that expected in offspring of an outbred pair. Most S. minutus colonies (34/41) were consistent with outbred biparental foundation. In three mature colonies, the genotypes of sterile castes suggested their origin by mixing of multiple related reproductives. Finally, four colonies in late stage of the colony life cycle contained sterile populations originating from multiple unrelated reproductives. We conclude that long-distance flights resulting in outbred reproduction are common in these soil-feeding species in pristine habitats but that other factors, such as mating preferences, could increase relatedness between founders. [ABSTRACT FROM AUTHOR]