The formation of spiral arms and rings in barred galaxies

We propose a theory to explain the formation of both spirals and rings in barred galaxies using a common dynamical framework. It is based on the orbital motion driven by the unstable equilibrium points of the rotating bar potential. Thus, spirals, rings and pseudo-rings are related to the invariant manifolds associated to the periodic orbits around these equilibrium points. We examine the parameter space of three barred galaxy models and discuss the formation of the different morphological structures according to the properties of the bar model. We also study the influence of the shape of the rotation curve in the outer parts, by making families of models with rising, flat or falling rotation curves in the outer parts. The differences between spiral and ringed structures arise from differences in the dynamical parameters of the host galaxies.Comment: 6 pages, 3 figures, conference proceedings of "Semaine de l'Astrophysique Francaise", Grenoble 2007, eds. J. Bouvier, A. Chalabaev, C. Charbonne

Superadiabatic spin-preserving control of a single-spin qubit in a double quantum dot with spin–orbit interaction

A protocol for controlling the localization of an electron with a fixed projection of spin between two quantum dots in a material with spin-orbit (SO) interaction is studied. Due to SO coupling, the manipulation of the electron shuttling between both quantum dots also leads to a mixing between spin projections near to the avoided crossing of levels. We use a transitionless quantum driving approach, neglecting SO interaction, to analytically design simple electric and magnetic pulses able to rapidly drive the electron along an adiabatic Landau–Zener manifold. We show that the same fields in the presence of SO interaction can also give a fast high-fidelity transition between the qubit states. The performance of the proposed protocol is assessed in the presence of SO interactions of typical semiconductor materials. It is shown that it provides a fast and efficient spin-conserving method for controlling the electron position in a double quantum dot.Fil: Gomez, Sergio Santiago. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; ArgentinaFil: Romero, Rodolfo Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; Argentin

The formation of spiral arms and rings in barred galaxies

In this and in a previous paper (Romero-Gomez et al. 2006) we propose a theory to explain the formation of both spirals and rings in barred galaxies using a common dynamical framework. It is based on the orbital motion driven by the unstable equilibrium points of the rotating bar potential. Thus, spirals, rings and pseudo-rings are related to the invariant manifolds associated to the periodic orbits around these equilibrium points. We examine the parameter space of three barred galaxy models and discuss the formation of the different morphological structures according to the properties of the bar model. We also study the influence of the shape of the rotation curve in the outer parts, by making families of models with rising, flat, or falling rotation curves in the outer parts. The differences between spiral and ringed structures arise from differences in the dynamical parameters of the host galaxies. The results presented here will be discussed and compared with observations in a forthcoming paper.Comment: 16 pages, 13 figures, accepted in A&A. High resolution version available at http://www.oamp.fr/dynamique/pap/merce.htm

Warp evidences in precessing galactic bar models

Most galaxies have a warped shape when they are seen from an edge-on point of view. The reason for this curious form is not completely known so far and in this work we apply dynamical system tools to contribute to its explanation. Starting from a simple, but realistic, model formed by a bar and a disc, we study the effect produced by a small misalignment between the angular momentum of the system and its angular velocity. To this end, a precession model is developed and considered, assuming that the bar behaves like a rigid body. After checking that the periodic orbits inside the bar keep being the skeleton of the inner system, even after inflicting a precession to the potential, we compute the invariant manifolds of the unstable periodic orbits departing from the equilibrium points at the ends of the bar to get evidences of their warped shapes. As it is well known, the invariant manifolds associated with these periodic orbits drive the arms and rings of barred galaxies and constitute the skeleton of these building blocks. Looking at them from a side-on viewpoint, we find that these manifolds present warped shapes as those recognized in observations. Lastly, test particle simulations have been performed to determine how the stars are affected by the applied precession, confirming this way the theoretical results obtained.Comment: 14 pages, 21 figures, Accepted for publication in A&A (15th Jan 2016

Popular representations of leadership: heroes and superheroes in times of crisis

The importance of popular culture in the study of politics–especially in the creation, development and propagation of political ideas–has scarcely been examined in any depth by students of politics. The cultural representations of political institutions and processes apparently escape the defined fields of the theoretical disciplines concerned with political phenomena. Political philosophy, particularly in the Englishspeaking world, has been largely committed in the last four decades to provide rationally compelling arguments aimed to justify the principles of political morality, detaching itself from concrete political experience and privileging instead an abstract, universal and ahistorical normative account of the ideal polity. Political theory has done no better is it tends to disintegrate itself in political science, becoming increasingly subservient of sociology and quantitative empirical explanations of political events and processes (Horton and Baumeister, 1996: 3-5)

A decade of murder and grief: Mexico\u27s drug war turns ten

A few weeks before the Mexico\u27s 2006 election, La Familia Michoacana - among the most vicious of Mexico\u27s major drug cartels - tossed five severed heads onto the dance floor of the Sol y Sombra night club in Uruapan, Michoacán, along with a message outlining its strategy for targeted killings, which it called divine justice

El Chapo, story of a kingpin - or why Trump\u27s plan to defeat Mexican cartels is doomed to fail

Infamous Mexican drug kingpin Joaquín Archivaldo Guzmán Loera - aka El Chapo - currently faces 17 drug trafficking, murder, kidnapping and money laundering charges in the US, accrued over the past quarter-century

How the US is outsourcing border enforcement to Mexico

In describing the complex relationship between the two countries, Jeffrey Davidow, American ambassador to Mexico from 1998 to 2002, spoke of the bear and the porcupine . The US is an arrogant bear, brawny and insensitive to Mexico\u27s concerns. Mexico is a resentful porcupine, paranoid about American plots to undermine its sovereignty

D.H. Lawrence\u27s plural jurisprudence: an enquiry into Desmond Manderson\u27s post-positivist \u27law and literature\u27

The border means more than a customs house, a passport officer, a man with a gun. Over there everything is going to be different; life is never going to be quite the same again after your passport has been stamped and you find yourself speechless among the money-changers. Graham Greene, The Lawless Roads This article draws on Desmond Manderson\u27s theorisation of ‘law and literature’ in order to undertake a jurisprudential reading of the last two ‘leadership novels’ that D.H. Lawrence published in the 1920s: Kangaroo and The Plumed Serpent. This reading demonstrates the strengths and weaknesses in Manderson\u27s methodology while simultaneously contextualising the experience of modernity through Lawrence\u27s Australian and Mexican narratives. In sum, the article tests Manderson\u27s (Australian) jurisprudential reading of Kangaroo with the troubled (Mexican) modernity that emerged from the Mexican Revolution, as it is channelled through The Plumed Serpent

Mexico elects a leftist president who welcomes migrants

Leftist Andrés Manuel López Obrador, a former Mexico City mayor and career outsider, won Mexico\u27s July 1 presidential election in a landslide. The US-Mexico relationship is about to change