Hybrid computer simulation of HVDC systems

Imperial Users onl

Image representation and compression via sparse solutions of systems of linear equations

We are interested in finding sparse solutions to systems of linear equations $mathbf{A}mathbf{x} = mathbf{b}$, where $mathbf{A}$ is underdetermined and fully-ranked. In this thesis we examine an implementation of the {em orthogonal matching pursuit} (OMP) algorithm, an algorithm to find sparse solutions to equations like the one described above, and present a logic for its validation and corresponding validation protocol results. The implementation presented in this work improves on the performance reported in previously published work that used software from SparseLab. We also use and test OMP in the study of the compression properties of $mathbf{A}$ in the context of image processing. We follow the common technique of image blocking used in the JPEG and JPEG 2000 standards. We make a small modification in the stopping criteria of OMP that results in better compression ratio vs image quality as measured by the structural similarity (SSIM) and mean structural similarity (MSSIM) indices which capture perceptual image quality. This results in slightly better compression than when using the more common peak signal to noise ratio (PSNR). We study various matrices whose column vectors come from the concatenation of waveforms based on the discrete cosine transform (DCT), and the Haar wavelet. We try multiple linearization algorithms and characterize their performance with respect to compression. An introduction and brief historical review on the topics of information theory, quantization and coding, and the theory of rate-distortion leads us to compute the distortion $D$ properties of the image compression and representation approach presented in this work. A choice for a lossless encoder $gamma$ is left open for future work in order to obtain the complete characterization of the rate-distortion properties of the quantization/coding scheme proposed here. However, the analysis of natural image statistics is identified as a good design guideline for the eventual choice of $gamma$. The lossless encoder $gamma$ is to be understood under the terms of a quantizer $(alpha, gamma, beta)$ as introduced by Gray and Neuhoff

At the Movies: Avoiding Head-to-Head Competition on the Big Screen: The Economics of Movie Distribution

This paper provides theoretical explanations for devices that movie distributors use to avoid head-to-head competition. We use a simple static model to show how revenuse sharing exhibition contracts providex multiplex owners with incentives to take cross effects on demand into account. Then we simulate a dynamic version of the model to explian the practice of staggering the release dates of hit movies and consider how vertical integration affects release patterns and the allocation of movies to screens. The dynamic model is of independent interest because it allows for dynamic strategic interaction in a common agency framework.common agent; exclusive dealing; entertainment; film; licensing

At the Movies: Risk Sharing and the Economics of Exhibition Contracts

The current literature on sharing contracts emphasizes the importance of asymmetric information and typically assumes that one party is risk neutral while the other is risk averse. This paper describes a real-world contract that is widely used - the movie exhibition contract - and argues that asymmetric information is not the main feature of the environment that leads to sharing. The explanation that fits the facts better is simply that distributors and exhibitors are both risk averse. The analysis suggests that two-sided risk aversion is important in determining contracts

At the Movies: Avoiding Head-to-Head Competition on the Big Screen: The Economics of Movie Distribution

This paper provides theoretical explanations for devices that movie distributors use to avoid head-to-head competition. We use a simple static model to show how revenuse sharing exhibition contracts providex multiplex owners with incentives to take cross effects on demand into account. Then we simulate a dynamic version of the model to explian the practice of staggering the release dates of hit movies and consider how vertical integration affects release patterns and the allocation of movies to screens. The dynamic model is of independent interest because it allows for dynamic strategic interaction in a common agency framework

Interacción, construcción del espacio social y sexualidad en el Metro de la Ciudad de México | Interaction, construction of social space and sexuality in Mexico City’s Subway

Este texto es un estudio de las interacciones sociales ocurridas en el Metro de la Ciudad de México. Es el resultado de un trabajo de campo de seis meses y se basa en la perspectiva analítica de la micro-sociología de Erving Gorffman y en la geografía social de Guy Di Meo. Propone una observación centrada en el cuerpo y sus gestos como medios de comunicación, así como formas de uso y transformación del espacio. En el caso del Metro de la Ciudad de México, esas expresiones están orientadas por la sexualidad y los roles de género que ella supone. Aunque en principio este medio de transporte es considerado un espacio público, los vínculos que los pasajeros establecen durante sus trayectos lo exhiben como un espacio más complejo, flexible y ambiguo, en donde es posible establecer relaciones tradicionalmente encasilladas en el ejercicio de lo privado

At the Movies: Risk Sharing and the Economics of Exhibition Contracts

The current literature on sharing contracts emphasizes the importance of asymmetric information and typically assumes that one party is risk neutral while the other is risk averse. This paper describes a real-world contract that is widely used - the movie exhibition contract - and argues that asymmetric information is not the main feature of the environment that leads to sharing. The explanation that fits the facts better is simply that distributors and exhibitors are both risk averse. The analysis suggests that two-sided risk aversion is important in determining contracts.principal agent; licensing; entertainment; film; rental