An analysis of overall network architecture reveals an infinite-period bifurcation underlying oscillation arrest in the segmentation clock

Unveiling the mechanisms through which the somitogenesis regulatory network exerts spatiotemporal control of the somitic patterning has required a combination of experimental and mathematical modeling strategies. Significant progress has been made for the zebrafish clockwork. However, due to its complexity, the clockwork of the amniote segmentation regulatory network has not been fully elucidated. Here, we address the question of how oscillations are arrested in the amniote segmentation clock. We do this by constructing a minimal model of the regulatory network, which privileges architectural information over molecular details. With a suitable choice of parameters, our model is able to reproduce the oscillatory behavior of the Wnt, Notch and FGF signaling pathways in presomitic mesoderm (PSM) cells. By introducing positional information via a single Wnt3a gradient, we show that oscillations are arrested following an infinite-period bifurcation. Notably: the oscillations increase their amplitude as cells approach the anterior PSM and remain in an upregulated state when arrested; the transition from the oscillatory regime to the upregulated state exhibits hysteresis; and an opposing distribution of the Fgf8 and RA gradients in the PSM arises naturally in our simulations. We hypothesize that the interaction between a limit cycle (originated by the Notch delayed-negative feedback loop) and a bistable switch (originated by the Wnt-Notch positive cross-regulation) is responsible for the observed segmentation patterning. Our results agree with previously unexplained experimental observations and suggest a simple plausible mechanism for spatiotemporal control of somitogenesis in amniotes.Comment: 11 pages, 5 figures, added references, added figures, extended supporting material, revised arguments in the discussion, corrected typo

About the isocurvature tension between axion and high scale inflationary models

The present work suggests that the isocurvature tension between axion and high energy inflationary scenarios may be avoided by considering a double field inflationary model involving the hidden Peccei-Quinn Higgs and the Standard Model one. Some terms in the lagrangian we propose explicitly violate the Peccei-Quinn symmetry but, at the present era, their effect is completely negligible. The resulting mechanism allows a large value for the axion constant, of the order $f_a\sim M_p$, thus the axion isocurvature fluctuations are suppressed even when the scale of inflation $H_{inf}$ is very high, of the order of $H_{inf}\sim M_{gut}$. This numerical value is typical in Higgs inflationary models. An analysis about topological defect formation in this scenario is also performed, and it is suggested that, under certain assumptions, their effect is not catastrophic from the cosmological point of view

MHD Remote Numerical Simulations: Evolution of Coronal Mass Ejections

Coronal mass ejections (CMEs) are solar eruptions into interplanetary space of as much as a few billion tons of plasma, with embedded magnetic fields from the Sun's corona. These perturbations play a very important role in solar--terrestrial relations, in particular in the spaceweather. In this work we present some preliminary results of the software development at the Universidad Nacional Autonoma de Mexico to perform Remote MHD Numerical Simulations. This is done to study the evolution of the CMEs in the interplanetary medium through a Web-based interface and the results are store into a database. The new astrophysical computational tool is called the Mexican Virtual Solar Observatory (MVSO) and is aimed to create theoretical models that may be helpful in the interpretation of observational solar data.Comment: 2 pages, 1 color figure. To appear in Proceedings IAU Symposium No. 259. Cosmic Magnetic Fields: From Planets, to Stars and Galaxies. In pres

Dynamic Stability and Thermodynamic Characterization in an Enzymatic Reaction at the Single Molecule Level

In this work we study, at the single molecular level, the thermodynamic and dynamic characteristics of an enzymatic reaction comprising a rate limiting step. We investigate how the stability of the enzyme-state stationary probability distribution, the reaction velocity, and its efficiency of energy conversion depend on the system parameters. We employ in this study a recently introduced formalism for performing a multiscale thermodynamic analysis in continuous-time discrete-state stochastic systems.Comment: In Press in Physica

Efecto-riqueza durante las Colocaciones Públicas Iniciales Privatizadoras en Chile (1984-1989)

Se estudia el desempeño posterior a la colocación de once Ofertas Públicas Iniciales (OPIs) en Chile, durante 1984-1989 y se proporciona una descripción detallada de las condiciones económicas y políticas prevalecientes. En particular, se presentan los detalles operativos del mecanismo de emisión de acciones, complementado con un estudio estadístico de los Rendimientos Ajustados por el Mercado de las OPIs. Aunque el tamaño de la muestra es limitado y no permite alcanzar una validez externa, el análisis confirma la presencia de patrones de desempeño muy similares a los observados en OPIs tanto privadas como privatizadoras, de acuerdo con otros estudios relacionados (Aggarwal, Leal y Hernández, 1993; Dewenter y Malatesta, 1997; Loughran, Ritter y Rydqvist, 1994; Perotti y Guney, 1993).

Oscillation arrest in the mouse somitogenesis clock presumably takes place via an infinite period bifurcation

In this work we address the question of how oscillations are arrested in the mouse somitogenesis clock when the determination front reaches presomitic cells. Based upon available experimental evidence we hypothesize that the mechanism underlying such a phenomenon involves the interaction between a limit cycle (originated by a delayed negative feedback loop) and a bistable switch (originated by a positive feedback loop). With this hypothesis in mind we construct the simplest possible model comprising both negative and positive feedback loops and show that (with a suitable choice of paremeters): 1) it can show an oscillatory behavior, 2) oscillations are arrested via an infinite-period bifurcation whenever the different gene-expression regulator-inputs act together in an additive rather than in a multiplicative fashion, and 3) this mechanism for oscillation arrest is compatible whit plentiful experimental observations.Comment: 13 pages, 2 figure

Banking Concentration in the European Union during the Last Fifteen Years

The increase in the concentration of the banking industry across European Union countries during the last fifteen years can be explained in terms of: a) global factors, like the comprehensive adoption of technological innovations, the intensification of competition that has resulted from the deregulation of the financial sector and, more recently, as a consequence of the government interventions and forced acquisitions prompted by the 2007-2009 financial crisis; and, b) factors that have been specific to the E.U., in particular, the structural changes that took place in the region as a result of the creation of the Single Financial Market (1993) and the introduction of the euro (1999). This work analyzes the concentration process of the banking industry in the E.U. during the last fifteen years giving preeminence to the strategic choices made by the region’s commercial banks. It also reports the most visible E.U. banks’ M&As and government interventions that resulted from the 2007-2009 financial crisis, make a preliminary evaluation of the outcomes, and suggests possible future trends for the banking industry in the region.Concentration in banking, European Union, M&As in banking

¿Puede vulnerarse la libertad de tránsito del propietario del predio sirviente al no permitírsele circular por una servidumbre de paso constituida sobre su predio a favor de otro? Comentario a la STC Exp. Nº 02006-2011-PHC/TC

En el presente trabajo la autora analiza una reciente sentencia emitida por el Tribunal Constitucional, la STC 02006-2011-PHC/TC, en la cual se discute si la libertad de tránsito de la propietaria del predio sirviente se encontraba vulnerada al no permitírsele el paso por una servidumbre constituida sobre su predio a favor de los titulares de los predios contiguos. Este fallo tiene gran relevancia práctica, pues la libertad de tránsito del titular del predio sirviente sólo podrá verse afectada cuando la servidumbre constituya el único acceso para ambos titulares (del predio sirviente y del predio dominante), más no cuando se acredite que el propietario del predio sirviente cuenta con otro acceso a los caminos públicos desde su propio predio. Para realizar este análisis, además se realiza un breve estudio doctrinario, legislativo y jurisprudencial del derecho fundamental a la libertad de tránsito y de las servidumbres de paso