Longitudinal flow and onset of deconfinement

The effects of the onset of deconfinement on longitudinal and transverse flow are studied. First, we analyze longitudinal pion spectra from $E_{\rm lab}= 2A$ GeV to $\sqrt{s_{\rm NN}}=200$ GeV within Landau's hydrodynamical model and the UrQMD transport approach. From the measured data on the widths of the pion rapidity spectra, we extract the sound velocity $c_s^2$ in the early stage of the reactions. It is found that the sound velocity has a local minimum (indicating a softest point in the equation of state, EoS) at $E_{\rm beam}=30A$ GeV. This softening of the EoS is compatible with the assumption of the formation of a mixed phase at the onset of deconfinement. Furthermore, the energy excitation function of elliptic flow ($v_2$) from $E_{\rm beam}=90A$ MeV to $\sqrt{s_{\rm NN}}=200$ GeV is explored within the UrQMD framework and discussed in the context of the available data. The transverse flow should also be sensitive to changes in the equation of state. Therefore, the underestimation of elliptic flow by the UrQMD model calculation above $E_{\rm lab}= 30A$ GeV might also be explained by assuming a phase transition from a hadron gas to the quark gluon plasma around this energy. This would be consistent with the model calculations, indicating a transition from hadronic matter to ``string matter'' in this energy range.Comment: Proceedings of the 3rd International Workshop The Critical Point and Onset of Deconfinement, Firenze, Ital

Internationalization Strategies of African MNEs: a case analysis of Angolan and Mozambican enterprises

Accepted manuscrip

The Internet as a catalyst for business internationalization in Africa

A lot of African internet-based MNEs have adopted an international marketing approach called glocalization – which describes products or services that are developed and distributed globally, but have also been customized to fit the local environment.Published versio

Seizing the 'Internet Plus' moment in Africa

https://www.researchgate.net/publication/292762551_Seizing_the_%27Internet_Plus%27_moment_in_AfricaPublished versionPublished versio

Numerical investigation of photon creation in a three-dimensional resonantly vibrating cavity: TE-modes

The creation of TE-mode photons in a three-dimensional perfectly conducting cavity with one resonantly vibrating wall is studied numerically. We show that the creation of TE-mode photons in a rectangular cavity is related to the production of massive scalar particles on a time-dependent interval. The equations of motion are solved numerically which allows to take into account the intermode coupling. We compare the numerical results with analytical predictions and discuss the effects of the intermode coupling in detail. The numerical simulations reveal that photon creation in a three-dimensional resonantly vibrating cavity can be maximized by arranging the size of the cavity such that certain conditions are realized. In particular, the creation of TE-mode photons in the lowest frequency mode $(1,1,1)$ is most efficient in a non-cubic cavity where the size of the non-dynamical dimensions is roughly 11 times larger than the size of the dynamical dimension. We discuss this effect and its relation to the intermode coupling in detail.Comment: 14 pages, 18 figures, revised version, typos corrected, references added, title changed with respect to older version, submitted to Phys. Rev.

On Convex Envelopes and Regularization of Non-Convex Functionals without moving Global Minima

We provide theory for the computation of convex envelopes of non-convex functionals including an l2-term, and use these to suggest a method for regularizing a more general set of problems. The applications are particularly aimed at compressed sensing and low rank recovery problems but the theory relies on results which potentially could be useful also for other types of non-convex problems. For optimization problems where the l2-term contains a singular matrix we prove that the regularizations never move the global minima. This result in turn relies on a theorem concerning the structure of convex envelopes which is interesting in its own right. It says that at any point where the convex envelope does not touch the non-convex functional we necessarily have a direction in which the convex envelope is affine.Comment: arXiv admin note: text overlap with arXiv:1609.0937