Qubit-oscillator concatenated codes: decoding formalism & code comparison

Concatenating bosonic error-correcting codes with qubit codes can substantially boost the error-correcting power of the original qubit codes. It is not clear how to concatenate optimally, given there are several bosonic codes and concatenation schemes to choose from, including the recently discovered GKP-stabilizer codes [arXiv:1903.12615] that allow protection of a logical bosonic mode from fluctuations of the mode's conjugate variables. We develop efficient maximum-likelihood decoders for and analyze the performance of three different concatenations of codes taken from the following set: qubit stabilizer codes, analog/Gaussian stabilizer codes, GKP codes, and GKP-stabilizer codes. We benchmark decoder performance against additive Gaussian white noise, corroborating our numerics with analytical calculations. We observe that the concatenation involving GKP-stabilizer codes outperforms the more conventional concatenation of a qubit stabilizer code with a GKP code in some cases. We also propose a GKP-stabilizer code that suppresses fluctuations in both conjugate variables and that can be initialized using only controlled-SUM and Hadamard gates, and formulate qudit versions of GKP-stabilizer codes.Comment: 17 pages, 5 figure

Does urban sprawl increase the costs of providing local public services? Evidence from Spanish municipalities

This paper examines the impact of urban sprawl, a phenomenon of particular interest in Spain, which is currently experiencing this process of rapid, low-density urban expansion. Many adverse consequences are attributed to urban sprawl (e.g., traffic congestion, air pollution and social segregation), though here we are concerned primarily with the rising costs of providing local public services. Our initial aim is to develop an accurate measure of urban sprawl so that we might empirically test its impact on municipal budgets. Then, we undertake an empirical analysis using a cross-sectional data set of 2,500 Spanish municipalities for the year 2003 and a piecewise linear function to account for the potentially nonlinear relationship between sprawl and local costs. The estimations derived from the expenditure equations for both aggregate and six disaggregated spending categories indicate that low-density development patterns lead to greater provision costs of local public services.En el presente trabajo se analiza el impacto de la dispersión urbana, un fenómeno de especial interés en España, donde destaca la rapidez con la que este proceso de desarrollo urbano de baja densidad esta teniendo lugar actualmente. A pesar de la diversidad de consecuencias atribuidas a la dispersión urbana (tales como congestión del tráfico, contaminación o segregación social), aquí nos centramos en analizar el incremento en el coste de provisión de los servicios públicos locales. Con este objetivo, en primer lugar definimos una medida precisa de dispersión urbana que nos permita analizar empíricamente su impacto sobre los presupuestos municipales. En segundo lugar, llevamos a cabo un análisis empírico con datos de corte transversal para 2.500 municipios españoles referidos al año 2003 y una función lineal por tramos que recoge la posible relación no lineal existente entre la dispersión urbana y los costes. Las estimaciones obtenidas para las ecuaciones de gasto tanto a nivel agregado como para las seis categorías de gasto consideradas muestran que los desarrollos urbanos de baja densidad incrementan el coste de provisión de los servicios públicos locales

Tax differentials and agglomeration economies in intraregional firm location

This paper analyses empirically how differences in local taxes affect the intraregional location of new manufacturing plants. These effects are examined within the random profit maximization framework while accounting for the presence of different types of agglomeration economies (localization/ urbanization/ Jacobs' economies) at the municipal level. We look at the location decision of more than 10,000 establishments locating between 1996 and 2003 across more than 400 municipalities in Catalonia, a Spanish region. It is necessary to restrict the choice set to the local labor market and, above all, to control for agglomeration economies so as to identify the effects of taxes on the location of new establishments.Este artículo analiza a nivel empírico el papel de los impuestos locales en la localización intra-regional de nuevos establecimientos manufactureros. Estos efectos son analizados en un modelo de maximización aleatoria de beneficios "random profit maximization", teniendo en cuenta la presencia de distintas economías de aglomeración (localización/ urbanización/ Jacobs) a nivel municipal. En concreto, estudiamos la decisión de localización de más de 10.000 nuevos establecimientos manufactureros, que se establecen en más 400 municipios de la región española de Cataluña. Para identificar el efecto de los impuestos locales en la localización de los nuevos establecimientos es preciso restringir el conjunto de elección al mercado de trabajo local y, sobretodo, controlar la presencia de economías de aglomeración

Prospectives

Tiré de: Prospectives, vol. 14, no 3, oct. 1978.Titre de l'écran-titre (visionné le 24 janv. 2013

Quantum Gravity and the Holographic Principle

In this thesis we study two different approaches to holography, and comment on the possible relation between them. The first approach is an analysis of the high-energy regime of quantum gravity in the eikonal approximation, where the theory reduces to a topological field theory. This is the regime where particles interact at high energies but with small momentum transfer. We do this for the cases of asymptotically dS and AdS geometries and find that in both cases the theory is topological. We discuss the relation of our solutions in AdS to those of Horowitz and Itzhaki. We also consider quantum gravity away from the extreme eikonal limit and explain the sense in which the covariance of the theory is equivalent to taking into account transfer of momentum. The second approach we pursue is the AdS/CFT correspondence. We provide a holographic reconstruction of the bulk space-time metric and of bulk fields on this space-time, out of conformal field theory data. Knowing which sources are turned on is sufficient in order to obtain an asymptotic expansion of the bulk metric and of bulk fields near the boundary to high enough order so that all infrared divergences of the on-shell action are obtained. We provide explicit formulae for the holographic stress-energy tensors associated with an arbitrary asymptotically AdS geometry. We also study warped compactifications, where our d-dimensional world is regarded as a slice of a (d+1)-dimensional space-time, and analyse in detail the question as to where the d-dimensional observer can find the information about the extra dimension.Comment: Ph. D. thesis, Spinoza Institute & ITP (Utrecht University), 132 page

Quadern de pràctiques d'hidrogeologia i recursos hídrics en format interactiu

En l'àmbit de les ciències de la terra es presenten de manera simultània el material cartogràfic, les bases de dades i els mètodes de càlcul numèric. El quadern de pràctiques en temàtica hidrogeològica, elaborat en format interactiu, reuneix cartografies, textos, imatges, bases de dades i fulls de càlcul destinats a permetre un millor desenvolupament dels exercicis proposats, disposant de tota la documentació necessària en un format de qualitat. Amb la finalitat de fer-ne més atractiva la realització als estudiants de matèries relacionades amb la hidrogeologia i els recursos hídrics, els exercicis han estat elaborats amb dades i problemàtiques reals i actuals de Catalunya, que permeten copsar la complexitat de la gestió hidrològica del país i valorar-ne el potencial i les limitacions.En el ámbito de las Ciencias de la Tierra, el material cartográfico, las bases de datos y los métodos de cálculo numérico se presentan de manera simultánea. El Cuaderno de Prácticas en materia hidrogeológica, elaborado en formato interactivo, reúne cartografías, textos, imágenes, bases de datos y hojas de cálculo destinadas a permitir un mejor desarrollo de los ejercicios propuestos, ofreciendo toda la documentación necesaria en un formato de calidad. Con el propósito de hacer más atractiva su realización a los estudiantes de materias relacionadas con la Hidrogeología y los recursos hídricos, los ejercicios se han elaborado a partir de datos y problemáticas reales y actuales de Cataluña, que permiten captar la complejidad de la gestión hidrológica del país y, al mismo tiempo, valorar su potencial y sus limitaciones.In the field of the earth sciences, cartographic material, databases and numerical calculation methods are presented simultaneously. This workbook of practical exercises on the topic of hydrogeology, developed to be interactive, includes maps, texts, images, databases and spreadsheets aimed at enabling students to better perform the proposed exercises, as they have all the documentation they need in a high-quality format. With the purpose of making it more interesting for students in fields related to hydrogeology and water resources, the exercises were developed using real and up-to-date data and problems in Catalonia, enabling us to capture the complexity of water management in the country and assess both its potential and its limitations

Clustering and the hyperbolic geometry of complex networks

Clustering is a fundamental property of complex networks and it is the mathematical expression of a ubiquitous phenomenon that arises in various types of self-organized networks such as biological networks, computer networks or social networks. In this paper, we consider what is called the global clustering coefficient of random graphs on the hyperbolic plane. This model of random graphs was proposed recently by Krioukov et al. as a mathematical model of complex networks, under the fundamental assumption that hyperbolic geometry underlies the structure of these networks. We give a rigorous analysis of clustering and characterize the global clustering coefficient in terms of the parameters of the model. We show how the global clustering coefficient can be tuned by these parameters and we give an explicit formula for this function.Comment: 51 pages, 1 figur

La actitud del alumnado frente a la escuela

Históricamente muchos autores han tratado el tema de la actitud del alumnado frente a la escuela y las motivaciones instrumentales y expresivas de éstos. Estas aportaciones se han desarrollado tanto desde un punto de vista teórico donde encontramos autores como Bernstein (1977), Merton (1938), Fernández Enguita (1988), Subirats y Alegre (2006) o Tarabini (2012); como desde un punto de vista empírico con Alegre y Benito (2012), Barbeta y Termes (2014) o Feito (2003). Siguiendo estas aportaciones, los objetivos de la presente comunicación son: 1.Realizar un breve recorrido por las aportaciones teóricas de diversos autores sobre la actitud del alumnado frente a la escuela y aportar algunas aclaraciones teóricas. 2.En base a esta revisión, se propone una tipología de actitudes frente a la escuela y su contrastación empírica. La comprobación empírica se ha realizado a partir del análisis de los datos de una muestra de 2000 estudiantes que cursaban 4º de ESO en 2013-14 o que habían nacido en el año 1998 y se encontraban en cursos inferiores, matriculados en 27 centros de la ciudad de Barcelona. Estos datos son el resultado de la primera fase de una investigación sobre las trayectorias formativas y laborales de los jóvenes que forma parte de un proyecto internacional de comparación entre ciudades sobre las prácticas educativas, las desigualdades educativas y las trayectorias de los jóvenes después de la escuela obligatoria.The aim of this communication is to explore and analyse students' motivations in compulsory education and examine whether these motivations affect differentially their future expectations. The concrete objectives of this study are twofold: 1.Explore previous empirical and empirical theoretical approaches on students' motivations and attitudes. 2.Propose a typology of attitudes towards the studies and characterize it according to sociodemographic variables and future expectations after compulsory education. The communication will show the results of one part of a larger piece of the International Study of City Youth (ISCY). This is an international longitudinal study of 10th Grade students to find out more about student journeys through school into further study, work and life beyond school. The first student survey was carried out in 27 schools in Barcelona and filled in by 2000 students in their last year of secondary compulsory education (4th ESO) or students born in 1998 (enrolled in lower courses that would correspond)

Inter-regional redistribution through infrastructure investment : tactical or programmatic?

In this paper we analyze the effects of both tactical and programmatic politics on the inter-regional allocation of infrastructure investment. We use a panel of data for the Spanish electoral districts during the period 1964-2004 to estimate an equation where investment depends both on economic and political variables. The results show that tactical politics do matter since, after controlling for economic traits, the districts with more 'Political power' still receive more investment. These districts are those where the incumbents' Vote margin of victory/ defeat in the past election is low, where the Marginal seat price is low, where there is Partisan alignment between the executives at the central and regional layers of government, and where there are Pivotal regional parties which are influential in the formation of the central executive. However, the results also show that programmatic politics matter, since inter-regional redistribution (measured as the elasticity of investment to per capita income) is shown to increase with the arrival of the Democracy and EU Funds, with Left governments, and to decrease the higher is the correlation between a measure of 'Political power' and per capita income