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We describe two fitting schemes that aim to represent the high-density part of realistic equations of state for numerical simulations such as neutron star oscillations. The low-density part of the equation of state is represented by an arbitrary polytropic crust, and we propose a generic procedure to stitch any desired crust to the high-density fit, which is performed on the internal energy, pressure and sound speed of barotropic equations of state that describe cold neutron stars in $\beta$-equilibrium. An extension of the fitting schemes to equations of state with an additional compositional argument is proposed. In particular we develop a formalism that ensures the existence of a $\beta$-equilibrium at low densities. An additional feature of this low-density model is that it can be, in principle, applied to any parametrization. The performance of the fits is checked on mass, radius and tidal deformability as well as on the dynamical radial oscillation frequencies. To that end, we use a pseudospectral isolated neutron star evolution code based on a non-conservative form of the hydrodynamical equations. A comparison to existing parametrizations is proposed, as far as possible, and to published radial frequency values in the literature. The static and dynamic quantities are well reproduced by the fitting schemes. Our results suggest that, even though the radius is very sensitive to the choice of the crust, this choice has little influence on the oscillation frequencies of a neutron star., Comment: 21 pages, 12 figures. This version matches the accepted version, with typos corrected

The unity of mathematics has its power to compactify experiences in a form capable of being transferred and modified or adapted to new mathematical situations. Yet, we believe that the phrase "Unity of Mathematics" expresses a dream, an ideal that doesn't exist. We shall point to diachronic and cross cultural disunities, to semantic, semiotic and philosophic ambiguities and to the non-acceptance of certain mathematical texts by some practitioners of the subject., Comment: 4 pages. This is a condensed, sharpened and polemic outcome of our previous discussions on that topic, disseminated in arXiv:1204.5143

Recent observations of the NN Serpentis post-common envelope binary system have revealed eclipse timing variations that have been attributed to the presence of two Jovian-mass exoplanets. Under the assumption that these planets are real and survived from the binary's Main Sequence state, we reconstruct initial binaries that give rise to the present NN Ser configuration and test the dynamical stability of the original system. Under standard assumptions about binary evolution, we find that survival of the planets through the entire Main Sequence life-time is very unlikely. Hence, we conclude that the planets are not survivors from before the Common Envelope phase, implying that either they formed recently out of material ejected from the primary, or that the observed signals are of non-planetary origin., Comment: 7 pages, 3 figures. Accepted to MNRAS

We describe and explain the desire, common among mathematicians, both for unity and independence in its major themes. In the dialogue that follows, we express our spontaneous and considered judgment and reservations by contrasting the development of mathematics as a goal-driven process as opposed to one that often seems to possess considerable arbitrariness., Comment: To the memory of Gian-Carlo Rota (April 27, 1932 - April 18, 1999), Contribution to the XI Oesterreichisches Symposion zur Geschichte der Mathematik, Organiser: Christa Binder, Topic: Der Blick aufs Ganze. Gibt es grosse Linien in der Entwicklung der Mathematik? Venue: Miesenbach (Austria), 22-28 April, 2012, 9 pages