Lifshitz Holography with Isotropic Scale Invariance

Is it possible for an anisotropic Lifshitz critical point to actually exhibit isotropic conformal invariance? We answer this question in the affirmative by constructing a concrete holographic realization. We study three-dimensional spin-3 higher-spin gauge theory with a z=2 Lifshitz ground state with non-trivial spin-3 background. We provide consistent boundary conditions and determine the associated asymptotic symmetry algebra. Surprisingly, we find that the algebra consists of two copies of the W_3 extended conformal algebra, which is the extended conformal algebra of an isotropic critical system. Moreover, the central charges are given by 3l/(2G). We consider the possible geometric interpretation of the theory in light of the higher spin gauge invariance and remark on the implications of the asymptotic symmetry analysis.Comment: 19 pp; v2: minor edits, new refs; v3: added footnote, minor rewordings, to appear in JHE

Improved operational limits for offshore pipelay vessels

Subsea pipelines are used extensively throughout the world’s oceans to transport oil and gas from offshore facilities to land, often hundreds of miles. These pipelines range in diameter from three to sixty inches and are installed in deeper depths every year, currently as deep as 2,900 meters. Pipeline construction and installation costs are a large percentage of offshore projects and thus, methods toward reducing costs is an imperative objective. With pipeline installation projects taking place in harsher environments, vessel operability is vital. This work presents an improved method for determining limiting criteria for pipelay operations to more effectively plan and execute offshore projects. This improvement is based on the consideration of total effective pipeline stresses as the limiting criterion rather than the traditionally used limiting pitch angle. Limiting sea curves based on a sample dynamic pipeline analysis are shown and their incorporation in workability planning is discussed

Evaluating the impact of urban mobility policies on the air quality levels of Barcelona by means of an integrated modelling system

Persistent high levels of NO2 have severe health effects on population. These are often found in large urban conurbations with high vehicle densities. In Barcelona, with one of the highest vehicle densities in Europe, the two traffic air quality monitoring stations are continuously exceeding the limit values established by the 2008/50/EC Ambient Air Quality Directive. To reduce traffic emissions and associated air pollution levels, Barcelona is applying a series of traffic restrictions that attempt to renew and reduce the amount of circulating vehicles within the city. These include the reduction of private vehicle space in specific areas or urban corridors of the city (superblocks and tactical urbanism) and the implementation of a Low Emission Zone (LEZ) that restricts the entrance of most polluting vehicles in the city. In order to quantify and evaluate the level of effectiveness of the applied restrictions, air quality modelling is presented as a necessary tool to complement the information provided by the air quality monitoring stations. In this sense, the present thesis evaluates the impact that the different restrictions have on the resulting NOx emissions and NO2 concentration levels in Barcelona. To accomplish that, we developed an integrated air quality system composed by the VISUM traffic simulator, the emission model HERMESv3 and the street-scale dispersion model CALIOPE-Urban, which integrates the mesoscale CALIOPE air quality forecast system and the Gaussian dispersion model R-LINE. The thesis first explains the coupling, calibration and validation process of the traffic-emission system. This is followed by an emission sensitivity analysis of typically high uncertainty emission features such as different approaches in regard of vehicle fleet composition, public bus transport implementation, temperature effect or the application of non-exhaust PM sources. We also explore the limitations of the developed macroscopic system by comparing it with a microscopic -highly detailed- approach composed by the microscopic traffic simulator Aimsun Next and the PHEMLight vehicle emission model. Finally, we explain the coupling of the traffic-emission system with the mesoscale CALIOPE and street-scale CALIOPE-Urban air quality systems. In this study, we apply the traffic restrictions previously mentioned in Barcelona to observe their effects in traffic routing, traffic emissions and resulting air quality levels at a resolution of 20 meters. Our results show that the only measures with an overall reduction on NOx emissions are the ones considering the LEZ or a reduction on the traffic demand of -25%. The combination of all strategies with the demand reduction shows the highest NOx emission decrease (-30%) while if traffic demand is kept constant, the computed NOx reductions are of -13%. The strategies limited to restrict the vehicle space on the city show a negligible impact on the overall traffic emissions (+0.1%), although they generate important street-level emission gradients, up to +/-17% in NOx. The impact on NO2 air quality levels follows the same pattern as for emissions. The scenarios comprising the LEZ and the -25% demand reduction show the highest NO2 reductions (-5 to -10 and -10 to -20 ug/m3 in daily average NO2 concentration values). The unique application of traffic measures limiting the vehicle space show limited impacts of +/-5 ug/m3 due to traffic re-routing, as previously commented. Considering the obtained results, the reductions achieved are insufficient to ensure compliant air quality levels, and are very far from reaching the new WHO air quality guideline values. The applied restrictions must be accompanied by a larger decrease in the total number of circulating vehicles throughout the city which could be achieved, for instance, by the application of a congestion charge, or the implementation of local zero emission zones similar to the ones that are currently being deployed in the city of London.La persistente acumulación de altos valores de NO2 presenta serios problemas de salud. Esto ocurre con frecuencia en grandes zonas urbanas con altas densidades de tráfico. En Barcelona, con una de las mayores densidades de vehículos de Europa, las dos estaciones monitoreo de calidad del aire de tráfico exceden de forma continuada los valores limite establecidos por la 2008/50/EC Ambient Air Quality Directive. Para reducir las emisiones de tráfico Barcelona esta aplicando una serie de restricciones al tráfico con el propósito de renovar y reducir la cantidad de vehículos circulante. Estas medidas incluyen la reducción de espacio al vehículo privado en áreas específicas o en corredores de la ciudad (Supermanzanas o urbanismo táctico) y la implementación de una Zona de Bajas Emisiones (ZBE) que restringe la entrada a los vehículos mas contaminantes. Para cuantificar y evaluar el nivel de eficacia de las restricciones mencionadas, la modelización de calidad del aire se presenta como una herramienta necesaria para complementar la información dada por las estaciones de monitoreo de calidad del aire. Esta tesis evalúa el impacto que las diferentes restricciones tienen en los valores de emisión de NOx y de concentración de NO2 en Barcelona. Para ello, hemos desarrollado un sistema de calidad del aire compuesto por el simulador de tráfico VISUM, el modelo de emisiones HERMESv3 y el modelo de dispersión urbana CALIOPE-Urban, que integra el sistema mesoescalar de calidad del aire CALIOPE y el sistema Gaussiano de dispersión R-LINE. En la tesis se detalla el acoplamiento y el proceso de calibración y validación del sistema de tráfico-emisiones. A continuación, se realiza un estudio de sensibilidad valorando diferentes aproximaciones de variables de alta incertidumbre para la estimación de emisiones tales como la composición vehicular, la implementación del transporte público, el efecto de la temperatura o la consideración de fuentes PM no provenientes del gas de escape. También exploramos las limitaciones del sistema macroscópico desarrollado comparándolo con un sistema de alto detalle compuesto por el simulador micro Aimsun Next y el modelo de emisiones vehiculares PHEMLight. Finalmente, explicamos el acoplamiento del sistema tráfico-emisiones con el sistema de calidad del aire mesoescalar CALIOPE y el urbano CALIOPE-Urban que usamos para evaluar las restricciones de tráfico antes mencionadas en Barcelona y observar sus efectos en las rutas de tráfico, emisiones y concentración a una resolución de 20 metros. Los resultados muestran que las únicas medidas con una reducción global de emisiones NOx son las que consideran la ZBE o una reducción de demanda del -25%. La combinación de todas las estrategias con la reducción de demanda muestra las mayores reducciones en NOx (-30%) mientras que si la demanda se mantiene constante las reducciones observadas son del -13%. Las estrategias que se limitan a restringir el espacio del vehículo muestran reducciones negligibles (+0.1%), aunque generan importantes gradientes a nivel de calle que pueden llegar al +/-17% en NOx. El impacto en los valores de concentración de NO2 sigue los mismos patrones que las emisiones. Los escenarios que comprenden la ZBE y la reducción de demanda del -25% muestran las mayores reducciones (-5 a -10 y -10 a -20 ug/m3 de NO2). La consideración de las medidas que únicamente limitan el espacio al vehículo muestran reducciones de NO2 de +/-5 ug/m3 debido a la redistribución de rutas de tráfico. Concluimos que las reducciones obtenidas son insuficientes para asegurar valores de calidad del aire conforme a los límites de la UE, y están muy lejos de llegar a los nuevos valores guía de la OMS. Las restricciones aplicadas deben ir acompañadas por un mayor descenso del total de vehículos circulantes que podría conseguirse, por ejemplo, mediante la aplicación de un peaje de congestión o la implementación de zonas de cero emisiones, similares a las que se están desplegando actualmente en la ciudad de LondresPostprint (published version

INNDAGA: an environmental data acquisition innovation platform

INNDAGA is a multipurpose platform for conducting oceanographic surveys in coastal areas developed on an 8.5 m long inflatable boat. This concept allows the vessel to operate safely and with great manoeuvring flexibility in areas where larger research vessels cannot access (rocky areas, port ...) at low operational cost. Is fully integrated in an information management system to providing efficiency and effectiveness of strategic decision making.Peer Reviewe

Usage-based and emergentist approaches to language acquisition

It was long considered to be impossible to learn grammar based on linguistic experience alone. In the past decade, however, advances in usage-based linguistic theory, computational linguistics, and developmental psychology changed the view on this matter. So-called usage-based and emergentist approaches to language acquisition state that language can be learned from language use itself, by means of social skills like joint attention, and by means of powerful generalization mechanisms. This paper first summarizes the assumptions regarding the nature of linguistic representations and processing. Usage-based theories are nonmodular and nonreductionist, i.e., they emphasize the form-function relationships, and deal with all of language, not just selected levels of representations. Furthermore, storage and processing is considered to be analytic as well as holistic, such that there is a continuum between children's unanalyzed chunks and abstract units found in adult language. In the second part, the empirical evidence is reviewed. Children's linguistic competence is shown to be limited initially, and it is demonstrated how children can generalize knowledge based on direct and indirect positive evidence. It is argued that with these general learning mechanisms, the usage-based paradigm can be extended to multilingual language situations and to language acquisition under special circumstances

The Middeck Active Control Experiment (MACE)

The Middeck Active Control Experiment (MACE) is a NASA In-Step and Control Structure Interaction (CSI) Office funded Shuttle middeck experiment. The objective is to investigate the extent to which closed-loop behavior of flexible spacecraft in zero-gravity (0-g) can be predicted. This prediction becomes particularly difficult when dynamic behavior during ground testing exhibits extensive suspension and direct gravity coupling. On-orbit system identification and control reconfiguration is investigated to improve performance which would otherwise be limited due to errors in prediction. The program is presently in its preliminary design phase with launch expected in the summer of 1994. The MACE test article consists of three attitude control torque wheels, a two axis gimballing payload, inertial sensors and a flexible support structure. With the acquisition of a second payload, this will represent a multiple payload platform with significant structural flexibility. This paper presents on-going work in the areas of modelling and control of the MACE test article in the zero and one-gravity environments. Finite element models, which include suspension and gravity effects, and measurement models, derived from experimental data, are used as the basis for Linear Quadratic Gaussian controller designs. Finite element based controllers are analytically used to study the differences in closed-loop performance as the test article transitions between the 0-g and 1-g environments. Measurement based controllers are experimentally applied to the MACE test article in the 1-g environment and achieve over an order of magnitude improvement in payload pointing accuracy when disturbed by a broadband torque disturbance. The various aspects of the flight portion of the experiment are also discussed

Basin structure of optimization based state and parameter estimation

Most data based state and parameter estimation methods require suitable initial values or guesses to achieve convergence to the desired solution, which typically is a global minimum of some cost function. Unfortunately, however, other stable solutions (e.g., local minima) may exist and provide suboptimal or even wrong estimates. Here we demonstrate for a 9-dimensional Lorenz-96 model how to characterize the basin size of the global minimum when applying some particular optimization based estimation algorithm. We compare three different strategies for generating suitable initial guesses and we investigate the dependence of the solution on the given trajectory segment (underlying the measured time series). To address the question of how many state variables have to be measured for optimal performance, different types of multivariate time series are considered consisting of 1, 2, or 3 variables. Based on these time series the local observability of state variables and parameters of the Lorenz-96 model is investigated and confirmed using delay coordinates. This result is in good agreement with the observation that correct state and parameter estimation results are obtained if the optimization algorithm is initialized with initial guesses close to the true solution. In contrast, initialization with other exact solutions of the model equations (different from the true solution used to generate the time series) typically fails, i.e. the optimization procedure ends up in local minima different from the true solution. Initialization using random values in a box around the attractor exhibits success rates depending on the number of observables and the available time series (trajectory segment).Comment: 15 pages, 2 figure