Single- and double-vortex vector solitons in self-focusing nonlinear media

We study two-component spatial optical solitons carrying an angular momentum and propagating in a self-focusing saturable nonlinear medium. When one of the components is small, such vector solitons can be viewed as a self-trapped vortex beam that guides either the fundamental or first-order guided mode, and they are classified as single- and double-vortex vector solitons. For such composite vortex beams, we demonstrate that a large-amplitude guided mode can stabilize the ring-like vortex beam which usually decays due to azimuthal modulational instability. We identify different types of these vector vortex solitons and demonstrate both vortex bistability and mutual stabilization effect.Comment: 7 pages, 13 figure

A note on covers of fibred hyperbolic manifolds

For each surface $S$ of genus $g>2$ we construct pairs of conjugate pseudo-Anosov maps, $\varphi_1$ and $\varphi_2$, and two non-equivalent covers $p_i: \tilde S \longrightarrow S$, $i=1,2$, so that the lift of $\varphi_1$ to $\tilde S$ with respect to $p_1$ coincides with that of $\varphi_2$ with respect to $p_2$. The mapping tori of the $\varphi_i$ and their lift provide examples of pairs of hyperbolic $3$-manifolds so that the first is covered by the second in two different ways.Comment: 9 pages, 2 figure

A comparative analysis of executive information systems in organisations in South Africa and Spain

Executive Information Systems (EIS) grew out of the information needs of executives and are designed to serve the needs of users in strategic planning and decision-making. EIS are high risk information technology (IT) implementation projects. With the emergence of global information technologies, existing paradigms are being altered which are spawning new considerations for IT implementation. Web-based technologies are causing a revisit to existing IT implementation models, including those for EIS. The authors compare two recent survey studies of EIS implementation in well-established organisations in South Africa and Spain. From a comparative analysis, the authors report six identified similarities and three differences in EIS in these countries