Complete factorization of equations of motion for generalized scalar field theories

We demonstrate that the complete factorization of equations of motion into first-order differential equations can be obtained for real and complex scalar field theories with non-canonical dynamics.Comment: 5 pages; version published in EP

Cell Therapy for Type 1 Diabetes

Acknowledgements The work described in this review was supported by a grant from the MRC. K.R.M. is supported by a fellowship from the Scottish Translational Medicines and Therapeutics Initiative through the Wellcome Trust.Peer reviewedPublisher PD

Dynamical complexity of discrete time regulatory networks

Genetic regulatory networks are usually modeled by systems of coupled differential equations and by finite state models, better known as logical networks, are also used. In this paper we consider a class of models of regulatory networks which present both discrete and continuous aspects. Our models consist of a network of units, whose states are quantified by a continuous real variable. The state of each unit in the network evolves according to a contractive transformation chosen from a finite collection of possible transformations, according to a rule which depends on the state of the neighboring units. As a first approximation to the complete description of the dynamics of this networks we focus on a global characteristic, the dynamical complexity, related to the proliferation of distinguishable temporal behaviors. In this work we give explicit conditions under which explicit relations between the topological structure of the regulatory network, and the growth rate of the dynamical complexity can be established. We illustrate our results by means of some biologically motivated examples.Comment: 28 pages, 4 figure

Asteroseismology and Magnetic Cycles

Small cyclic variations in the frequencies of acoustic modes are expected to be a common phenomenon in solar-like pulsators, as a result of stellar magnetic activity cycles. The frequency variations observed throughout the solar and stellar cycles contain information about structural changes that take place inside the stars as well as about variations in magnetic field structure and intensity. The task of inferring and disentangling that information is, however, not a trivial one. In the sun and solar-like pulsators, the direct effect of the magnetic field on the oscillations might be significantly important in regions of strong magnetic field (such as solar- / stellar-spots), where the Lorentz force can be comparable to the gas-pressure gradient. Our aim is to determine the sun- / stellar-spots effect on the oscillation frequencies and attempt to understand if this effect contributes strongly to the frequency changes observed along the magnetic cycle. The total contribution of the spots to the frequency shifts results from a combination of direct and indirect effects of the magnetic field on the oscillations. In this first work we considered only the indirect effect associated with changes in the stratification within the starspot. Based on the solution of the wave equation and the variational principle we estimated the impact of these stratification changes on the oscillation frequencies of global modes in the sun and found that the induced frequency shifts are about two orders of magnitude smaller than the frequency shifts observed over the solar cycle.Comment: 4 pages, 6 figures, ESF Conference: The Modern Era of Helio- and Asteroseismology, to be published on 3 December 2012 at Astronomische Nachrichten 333, No. 10, 1032-103

Cosmic voids in modified gravity scenarios

Modified gravity (MG) theories aim to reproduce the observed acceleration of the Universe by reducing the dark sector while simultaneously recovering General Relativity (GR) within dense environments. Void studies appear to be a suitable scenario to search for imprints of alternative gravity models on cosmological scales. Voids cover an interesting range of density scales where screening mechanisms fade out, which reaches from a density contrast $\delta \approx -1$ close to their centers to $\delta \approx 0$ close to their boundaries. We present an analysis of the level of distinction between GR and two modified gravity theories, the Hu-Sawicki $f(R)$ and the symmetron theory. This study relies on the abundance, linear bias, and density profile of voids detected in n-body cosmological simulations. We define voids as connected regions made up of the union of spheres with a {\it \textup{mean}} density given by $\overline\rho_v=0.2\,\overline\rho_m$, but disconnected from any other voids. We find that the height of void walls is considerably affected by the gravitational theory, such that it increases for stronger gravity modifications. Finally, we show that at the level of dark matter n-body simulations, our constraints allow us to distinguish between GR and MG models with $|f_{R0}| > 10^{-6}$ and $z_{SSB} > 1$. Differences of best-fit values for MG parameters that are derived independently from multiple void probes may indicate an incorrect MG model. This serves as an important consistency check.Comment: 15 pages, 12 figure

Effects of rotation in the energy spectrum of C60C_{60}

In this paper, motivated by the experimental evidence of rapidly rotating $C_{60}$ molecules in fullerite, we study the low-energy electronic states of rotating fullerene within a continuum model. In this model, the low-energy spectrum is obtained from an effective Dirac equation including non-Abelian gauge fields that simulate the pentagonal rings of the molecule. Rotation is incorporated into the model by solving the effective Dirac equation in the rotating referential frame. The exact analytical solution for the eigenfunctions and energy spectrum is obtained, yielding the previously known static results in the no rotation limit. Due to the coupling between rotation and total angular momentum, that appears naturally in the rotating frame, the zero modes of static $C_{60}$ are shifted and also suffer a Zeeman splitting whithout the presence of a magnetic field