Interaction Topologies and Information Flow

Networks are ubiquitous, underlying systems as diverse as the Internet, food webs, societal interactions, the cell, and the brain. Of crucial importance is the coupling of network structure with system dynamics, and much recent attention has focused on how information, such as pathogens, mutations, or ideas, ow through networks. In this dissertation, we advance the understanding of how network structure a ects information ow in two important classes of models. The rst is an independent interaction model, which is used to investigate the propagation of advantageous alleles in evolutionary algorithms. The second is a threshold model, which is used to study the dissemination of ideas, fads, and innovations throughout populations. This journal-format dissertation comprises three interrelated studies, in which we investigate the in uence of network structure on the dynamical properties of information ow. In the rst study, we develop an analytical technique to approximate system dynamics in arbitrarily structured regular interaction topologies. In the second study, we investigate the ow of advantageous alleles in degree-correlated scale-free population structures, and provide a simple topological metric for assessing the selective pressures induced by these networks. In the third study, we characterize the conditions in which global information cascades occur in threshold models of binary decisions with externalities, structured on degree-correlated Poisson-distributed random networks

Identification and Inference in First-Price Auctions with Risk Averse Bidders and Selective Entry

We study identification and inference in first-price auctions with risk averse bidders and selective entry, building on a flexible entry and bidding framework we call the Affiliated Signal with Risk Aversion (AS-RA) model. Assuming that the econometrician observes either exogenous variation in the number of potential bidders (N) or a continuous instrument (z) shifting opportunity costs of entry, we provide a sharp characterization of the nonparametric restrictions implied by equilibrium bidding. Given variation in either competition or costs, this characterization implies that risk neutrality is nonparametrically testable in the sense that if bidders are strictly risk averse, then no risk neutral model can rationalize the data. In addition, if both instruments (discrete N and continuous z) are available, then the model primitives are nonparametrically point identified. We then explore inference based on these identification results, focusing on set inference and testing when primitives are set identified. Keywords: Auctions, entry, risk aversion, identification, set inference

Productivity dynamics of the UK economy: a micro data perspective

This dissertation analyzes two factors which may lie behind the recent productivity surge in the US, the lack of productivity growth in Europe and, ultimately, the persistence of significative differences in the levels of productivity across the two macro areas. First, we analyse the role played by Information Technologies (IT). Second, we study the impact of specific regulatory policies, focusing on the consequences of regulations which constrain the entry of large and peripheral retail stores ("big-boxes"). These issues are explored in the context of the UK economy, whose recent economic performance is consistent with the overall European picture of sluggish productivity growth (Basu et al., 2003). Furthermore, the questions are approached from a micro data perspective, using a series of novel establishment and firm-level datasets drawn from Census data sources. In the first two essays I focus on the role played by Information Technologies (IT), which appear to have played a substantial role in driving the recent productivity surge of the US economy. Chapter I sets out a theoretical and empirical context in which to study the impact of IT on productivity. Chapter II discusses the effects of IT on a large panel of firms active in the UK economy, observed between 1995 and 2003. A key finding of the study is the apparent ability of US multinationals to obtain higher productivity than non-US multinationals (and domestic UK establishments) from their IT capital. Chapter III, IV and V are dedicated to the study of the retail industry, which accounts for a large part of the European productivity gap vis a vis the US over the past decade. In particular, we study the effect of entry regulations against large retail stores ("big-boxes"). In Chapter III, it is shown that the recent introduction of entry regulations against large stores in the UK has paradoxically increased the competition faced by mom and pops retailers. Chapter IV show evidence that entry regulations have also significantly lowered the productivity of UK retail chains, forcing them to operate at a lower scale of retail activity. This result is set in an international context in Chapter V, where the market structure and the productivity dynamics of the UK retail industry with that of the US and Japan are compared using novel Census data sources

Diffusion, Absorbing States, and Nonequilibrium Phase Transitions in Range Expansions and Evolution

The spatial organization of a population plays a key role in its evolutionary dynamics and growth. In this thesis, we study the dynamics of range expansions, in which populations expand into new territory. Focussing on microbes, we first consider how nutrients diffuse and are absorbed in a population, allowing it to grow. These nutrients may be absorbed before reaching the population interior, and this "nutrient shielding" can confine the growth to a thin region on the population periphery. A thin population front implies a small local effective population size and enhanced number fluctuations (or genetic drift). We then study evolutionary dynamics under these growth conditions. In particular, we calculate the survival probability of mutations with a selective advantage occurring at the population front for two-dimensional expansions (e.g., along the surface of an agar plate), and three-dimensional expansions (e.g., an avascular tumor). We also consider the effects of irreversible, deleterious mutations which can lead to the loss of the advantageous mutation in the population via a "mutational meltdown," or non-equilibrium phase transition. We examine the effects of an inflating population frontier on the phase transition. Finally, we discuss how spatial dimension and frontier roughness influence range expansions of mutualistic, cross-feeding variants. We find here universal features of the phase diagram describing the onset of a mutualistic phase in which the variants remain mixed at long times.Physic

Stochastic Real-time Optimal Control: A Pseudospectral Approach for Bearing-Only Trajectory Optimization

A method is presented to couple and solve the optimal control and the optimal estimation problems simultaneously, allowing systems with bearing-only sensors to maneuver to obtain observability for relative navigation without unnecessarily detracting from a primary mission. A fundamentally new approach to trajectory optimization and the dual control problem is developed, constraining polynomial approximations of the Fisher Information Matrix to provide an information gradient and allow prescription of the level of future estimation certainty required for mission accomplishment. Disturbances, modeling deficiencies, and corrupted measurements are addressed with recursive updating of the target estimate with an Unscented Kalman Filter and the optimal path with Radau pseudospectral collocation methods and sequential quadratic programming. The basic real-time optimal control (RTOC) structure is investigated, specifically addressing limitations of current techniques in this area that lose error integration. The resulting guidance method can be applied to any bearing-only system, such as submarines using passive sonar, anti-radiation missiles, or small UAVs seeking to land on power lines for energy harvesting. Methods and tools required for implementation are developed, including variable calculation timing and tip-tail blending for potential discontinuities. Validation is accomplished with simulation and flight test, autonomously landing a quadrotor helicopter on a wire

ANALYSIS OF FLUID-MECHANICAL EFFICIENCY OF OFFSHORE WIND TURBINES FROM REGIONAL TO LOCAL SCALE

2013/2014Renewable energy resources, such as wind, are available worldwide. Locating areas with high and continual wind sources are crucial in pre-planning of wind farms. Vast offshore areas are characterized with higher and more reliable wind resources in comparison with continental areas. However, offshore wind energy production is in a quite preliminary phase. Elaborating the potential productivity of wind farms over such areas is challenging due to sparse in situ observations. Mediterranean basin is not an exception. The overall aim of this thesis is to perform analysis in model efficiency in estimation of wind energy from regional to local scale. First, we are proposing numerical simulations of near-surface wind fields from regional climate models (RCMs) in order to obtain and fill the gaps in observations over the Mediterranean basin. Four simulations produced with two regional climate models are examined. Remote sensing observations (QuikSCAT satellite) are used to assess the skill of the simulated fields. A technique in estimation the potential energy from the wind fields over the region is introduced locating the three potentially interesting sub-regions for wind farms. Then, we use local-scale model (large-eddy simulation) with implemented parameterization of wind turbine in order to simulate real case flow in theoretical wind farm. Information reported with regional climate model would be used to create inflow conditions for the selected sub-region of the Mediterranean Sea for simulating theoretical offshore wind farm. Finally, we would compare the estimation of wind power potential obtained by regional climate model and power production of theoretical wind farm obtained with large-eddy simulations for chosen sub-region. Within this multi-scale approach, we would present different numerical computational efficiency in application of wind energy and justification in usage of both regional and local scale models. The novelty of this multi-model methodological approach could be considered in offering significant information for wind industry.XXVII Ciclo198

The Black Book of Quantum Chromodynamics

The LHC (Large Hadron Collider) will serve as the energy frontier for high-energy physics for the next 20 years. The highlight of the LHC running so far has been the discovery of the Higgs boson, but the LHC programme has also consisted of the measurement of a myriad of other Standard Model processes, as well as searches for Beyond-the-Standard-Model physics, and the discrimination between possible new physics signatures and their Standard Model backgrounds. Essentially all of the physics processes at the LHC depend on quantum chromodynamics, or QCD, in the production, or in the decay stages, or in both. This book has been written as an advanced primer for physics at the LHC, providing a pedagogical guide for the calculation of QCD and Standard Model predictions, using state-of-the-art theoretical frameworks. The predictions are compared to both the legacy data from the Tevatron, as well as the data obtained thus far from the LHC, with intuitive connections between data and theory supplied where possible. The book is written at a level suitable for advanced graduate students, and thus could be used in a graduate course, but is also intended for every physicist interested in physics at the LHC