Revisiting the optical PTPT-symmetric dimer

Optics has proved a fertile ground for the experimental simulation of quantum mechanics. Most recently, optical realizations of $\mathcal{PT}$-symmetric quantum mechanics have been shown, both theoretically and experimentally, opening the door to international efforts aiming at the design of practical optical devices exploiting this symmetry. Here, we focus on the optical $\mathcal{PT}$-symmetric dimer, a two-waveguide coupler were the materials show symmetric effective gain and loss, and provide a review of the linear and nonlinear optical realizations from a symmetry based point of view. We go beyond a simple review of the literature and show that the dimer is just the smallest of a class of planar $N$-waveguide couplers that are the optical realization of Lorentz group in 2+1 dimensions. Furthermore, we provide a formulation to describe light propagation through waveguide couplers described by non-Hermitian mode coupling matrices based on a non-Hermitian generalization of Ehrenfest theorem.Comment: 25 pages, 12 figure

Challenges for Colombian medical journals

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Impact of Climate Change on Zoonotic Diseases in Latin America

La Convención Marco de Naciones Unidas sobre el Cambio Climático (CMNUCC), con sede en Bonn, Alemania, define el cambio climático como "un cambio de clima atribuido directa o indirectamente a la actividad humana que altera la composición de la atmósfera mundial y que se suma a los recursos naturales variabilidad del clima observada durante períodos de tiempo comparables ". Aunque muchas otras definiciones se pueden encontrar y se han declarado por muchos autores y grupos de investigación, el mensaje clave importante, es que el cambio climático supone una seria amenaza para el mundo, que puede generar agitación social, los desplazamientos de población, las dificultades económicas y ambientales la degradación, entre muchas otras consecuencias relevantes. Con el fin de llegar a un verde como World menos impacto antropogénico, de acuerdo con las nuevas tendencias ecológicas en la sociedad, la mitigación del cambio climático debe ser una prioridad para la sociedad y sus gobiernos (Rodríguez-Morales, 2011). Como se ha indicado anteriormente, el cambio climático ya es un problema ampliamente conocido por múltiples disciplinas (Rodríguez-Morales, 2005). Aunque sus orígenes pueden converger en un complejo de múltiples fenómenos de interacción, para algunas disciplinas, como las ciencias biológicas y médicas, sus consecuencias son más estudiados y destacan por sus implicaciones actuales y más.Aún más, sus impactos y chillidos son motivo de preocupación a nivel global (Rodríguez-Morales et al, 2010 ). Esta amenaza creciente constituye en el siglo XXI un reto importante para la humanidad. Sus efectos aún son muchos los aspectos que se han estudiado no por la sociedad en diferentes niveles.The United Nations Framework Convention on Climate Change (UNFCC), located in Bonn,Germany, defines climate change as “a change of climate which is attributed directly or indirectly to human activity that alters the composition of global atmosphere and which is in addition to natural climate variability observed over comparable time periods”. Although many other definitions can be found and have been stated by many authors and research groups, the important key message, is that global climate change poses a serious threat to the World, which can generate social upheaval, population displacement, economic hardships, and environmental degradation, among many other relevant consequences. In order to reach a green as less anthropogenically impacted World, according to the new ecological trends in the society, mitigation of global climate change should be a priority for the society and its governments (Rodriguez-Morales, 2011). As has been previously stated, climate change is already a widely known problem to multiple disciplines (Rodriguez-Morales, 2005). Although its origins can converge in a complex of multiple interacting phenomena, for some disciplines, such as biological and medical sciences, their consequences are more studied and highlighted for their current and further implications. Even more, its impacts and squeals are cause of concern at a global level (Rodriguez-Morales et al, 2010). This growing threat represents in the XXI century a significant challenge for the humankind. Its effects even include many aspects that have been not studied by the society at different levels

Pulsations in M dwarf stars

We present the results of the first theoretical non-radial non-adiabatic pulsational study of M dwarf stellar models with masses in the range 0.1 to 0.5M_solar. We find the fundamental radial mode to be unstable due to an \epsilon mechanism caused by deuterium (D-) burning for the young 0.1 and 0.2M_solar models, by non-equilibrium He^3 burning for the 0.2 and 0.25M_solar models of 10^4Myr, and by a flux blocking mechanism for the partially convective 0.4 and 0.5M_solar models once they reach the age of 500Myr. The periods of the overstable modes excited by the D-burning are in the range 4.2 to 5.2h for the 0.1M_solar models and is of order 8.4h for the 0.2M_solar models. The periods of the modes excited by He^3 burning and flux blocking are in the range 23 to 40min. The more massive and oldest models are more promising for the observational detection of pulsations, as their ratio of instability e-folding time to age is more favourable.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in MNRAS Letters on 2011 October 11 Version 2 is the accepted manuscript with changes in boldfac