Distribución cuántica de claves en redes de acceso WDM-PON

En esta comunicación se plantea el estudio de redes para QKD donde sólo coexisten canales cuánticos compartiendo la misma fibra. Se han estudiado las redes de acceso basadas en la tecnología WDM-PON y DWDM (Dense WDM) en red central, lo que permitiría el direccionamiento mediante longitud de onda y abaratar la tecnología al compartir un solo sustrato físico, idéntico al usado en redes de telecomunicación, entre multitud de canales cuánticos. Además, hemos comprobado su funcionamiento de forma experimental en el laboratorio con equipos comerciales. En un futuro habrá que estudiar el comportamiento de los distintos componentes de la red y la compatibilidad de los distintos dispositivos QKD para integrarse dentro de un canal compartido en la misma red cuántica.

Multiplexing QKD systems in Conventional Optical Networks

Current QKD designs try to keep the quantum channel as error free as possible by using a separate physical medium for this purpose. In the most common case, this means the exclusive use of an optical fiber for the quantum channel, precluding its use for any other purpose. In current optical networks, the fiber is the single most expensive element and this poses a major problem from a cost and availability point of view. Sharing the fiber is thus mandatory for the widespread adoption of QKD. The objective of this communication is to propose a general scheme and present some preliminary measurements of a metropolitan area network (MAN) designed to multiplex of the order of 64 addressable quantum channels and the associated QKD classical service signals on a single dark fibre. It uses as much existing components and infraestructure as possible in an attempt to simultaneously lower most of the practical barriers for the adoption of QKD.

Proposal for a Wavelength Multiplexed Quantum Metropolitan Area Network

Quantum Key Distribution (QKD) is maturing quickly. However, the current approaches to its network use require conditions that make it an expensive technology. All the QKD networks deployed to date are designed as a collection of dedicated point-to-point links that use the trusted repeater paradigm. Instead, we propose a novel network model in which QKD systems use simultaneously quantum and conventional signals that are wavelength multiplexed over a common communication infrastructure. Signals are transmitted end-to-end within a metropolitan area using optical components. The model resembles a commercial telecom network and takes advantage of existing components, thus allowing for a cost-effective and reliable deployment.

Quantum metropolitan optical network based on wavelength division multiplexing

Quantum Key Distribution (QKD) is maturing quickly. However, the current approaches to its application in optical networks make it an expensive technology. QKD networks deployed to date are designed as a collection of point-to-point, dedicated QKD links where non-neighboring nodes communicate using the trusted repeater paradigm. We propose a novel optical network model in which QKD systems share the communication infrastructure by wavelength multiplexing their quantum and classical signals. The routing is done using optical components within a metropolitan area which allows for a dynamically any-to-any communication scheme. Moreover, it resembles a commercial telecom network, takes advantage of existing infrastructure and utilizes commercial components, allowing for an easy, cost-effective and reliable deployment.

Grafías en la piel de la ciudad : graffiti y pintadas comerciales como expresiones sociales reflejadas en las calles de Medellín - Colombia

EL FENÓMENO DE LAS GRAFÍAS EN LA CIUDAD ACTUAL. Este ensayo es resultado de una investigación de tesis doctoral acerca de las intervenciones gráficas en el espacio público en la ciudad de Medellín, Colombia. Nos hemos centrado en dos tipos de accionar: por una parte las intervenciones gráficas que se corresponden al ámbito comercial y, por la otra, las que se alejan de éste para introducirse en los campos del graffiti y sus variantes, pero donde todas tiene algo en común, el cerramiento arquitectónico y de infraestructuras como soporte. La metodología parte de un trabajo de campo donde se recopila en imágenes la variedad de tipologías gráficas encontradas en la ciudad, para a continuación problematizar sus resultados como conflictos por el uso del espacio público; las valoraciones han sido extraídas de los discursos de sus autores, construidas con el formato de entrevista. Los resultados son un viaje a través de las particularidades de los gestos estéticos, que difieren en cuanto técnicas, motivaciones, imágenes resultantes en un espacio público cargado de re-construcciones simbólicas, que nos llevan al establecimiento de nuevos espacios de comunicación social. Sus conclusiones van encaminadas a la concepción de un espacio público vital para los ciudadanos que, dentro o al margen de los dispositivos de control social, lo apropian para dotarlos de nuevos significados, a la vez que lo proveen de diversas, divergentes y a veces conflictivas configuraciones estéticas. Palabras claves: graffiti, publicidad, espacio público, ciudad, Medellín. ABSTRACT THE PHENOMENON OF THE WRITINGS IN THE CONTEMPORARY CITY. This essay is the result of a research done for my doctoral thesis on the graphic interventions in public spaces in the city of Medellin, Colombia. We focused on two types of actions: the first graphic interventions correspond to the commercial sector and, the second, to those that differ from it to get into the fields of graffiti and its variants, but they all have something in common, the architectural cladding and infrastructure as their support. The methodology begins as a field work where images are collected in a variety of graphic typologies found in the city, and then to problematize their results such as the conflicts over the use of public space; the assessment has been drawn from the speeches of their authors and built through interviews. The results are a journey all the way through the particularities of aesthetic gestures, which differ in techniques, motivations, resulting images in a public space full of symbolic re-building, that lead to the establishment of new spaces for social communication. The conclusions are aimed at conceiving a vital space for citizens that, whether they are within or outside the mechanisms of social control, take over to give it new meanings, as well as providing the public space with different, divergent and sometimes conflicting aesthetic configurations. Keywords: graffiti, advertising, public space, city, Medellin.

Global air-sea flux of CO2: An estimate based on measurements of sea–air pCO2 difference

Approximately 250,000 measurements made for the pCO2 difference between surface water and the marine atmosphere, ΔpCO2, have been assembled for the global oceans. Observations made in the equatorial Pacific during El Nino events have been excluded from the data set. These observations are mapped on the global 4° × 5° grid for a single virtual calendar year (chosen arbitrarily to be 1990) representing a non-El Nino year. Monthly global distributions of ΔpCO2 have been constructed using an interpolation method based on a lateral advection–diffusion transport equation. The net flux of CO2 across the sea surface has been computed using ΔpCO2 distributions and CO2 gas transfer coefficients across sea surface. The annual net uptake flux of CO2 by the global oceans thus estimated ranges from 0.60 to 1.34 Gt-C⋅yr−1 depending on different formulations used for wind speed dependence on the gas transfer coefficient. These estimates are subject to an error of up to 75% resulting from the numerical interpolation method used to estimate the distribution of ΔpCO2 over the global oceans. Temperate and polar oceans of the both hemispheres are the major sinks for atmospheric CO2, whereas the equatorial oceans are the major sources for CO2. The Atlantic Ocean is the most important CO2 sink, providing about 60% of the global ocean uptake, while the Pacific Ocean is neutral because of its equatorial source flux being balanced by the sink flux of the temperate oceans. The Indian and Southern Oceans take up about 20% each.