We study the role played by bilinguals in the competition between two languages and in the formation of a bilingual community. To this aim we introduce a simple three-state model that combines the Minett-Wang model, in which the bilinguals do not affect directly the probability of transition of an individual from monolingualism to bilingualism, and the Baggs-Freedman model, in which such a tran...

We focused on how repeat collaborations in projects for inventions affect performance. Repeat collaborations have two contradictory aspects. A positive aspect is team development or experience, and a negative aspect is team degeneration or decline. Since both contradicting phenomena are observed, inventors have a dilemma as to whether they should keep collaborating in a team or not. The dilemma...

The results of experiments in developing a method for extracting three-dimensional information from a scene by means of a polarimetric passive imaging sensor are summarized. This sensor provides a full Stokes vector at each sensor pixel location from which degree and angle of linear polarization are computed. The angle of linear polarization provides the azimuth angle of the surface normal vect...

This article addresses the current state of the art of technology in three-dimensional echocardiography as it applies to transducer design, beam forming, display, and quantification. Because three-dimensional echocardiography encompasses many technical and clinical areas, this article reviews its strengths and limitations and concludes with an analysis of what to use when.

represent in renewal theory the elapsed lifetimes of the "item in use" at time t. The limiting behavior of Y% as t—* °° has been extensively studied; if ju = £(X¿) < oo, Yt itself has a limiting distribution [8; 2] while if p= oo, the generalized arc-sine laws emerge as the possible limit distributions of Yt/t [2; 6]. It may be remarked that Yt forms a Markov process with right-continuous path ...

By international standards the economy of South Africa is extremely energy intensive with only a few countries having higher intensities. SA’s primary energy use per unit of GDP is amongst the highest in the world The high energy and electricity intensity of the economy partly reflects SA’s resource endowments (in particular the abundance of coal) but is also a function of the historical under-...

This paper considers some fundamental questions concerning marginally trapped surfaces, or apparent horizons, in Cauchy data sets for the Einstein equation. An area estimate for outermost marginally trapped surfaces is proved. The proof makes use of an existence result for marginal surfaces, in the presence of barriers, curvature estimates, together with a novel surgery construction for margina...

The surface alignment of lyotropic chromonic liquid crystals can not only be planar (tangential) but also homeotropic, with self-assembled aggregates perpendicular to the substrate, as demonstrated by mapping optical retardation and by three-dimensional imaging of the director field. With time, the homeotropic nematic undergoes a transition into a tangential state. The anchoring transition is d...