Phénomènes ondulatoires dans les lignes d'admission d'air et leur influence sur les performances des moteurs à combustion interne

L'onde engendrée par le piston pendant la phase d'admission se propage dans le conduit d'air frais et revient au cylindre par réflexions. Les phénomènes acoustiques augmentent jusqu'à 30% la quantité d'air admise par le moteur. La propagation acoustique dans les conduits portant un écoulement moyen turbulent est modélisée en une et trois dimensions. L'impédance d'entrée calculée est comparée aux résultats d'un dispositif expérimental innovant. Une nouvelle méthode de mesure des matrices de transfert en absence d'écoulement est également mise au point. Un couplage non-linéaire de l'impédance d'entrée du circuit d'air avec la chambre de combustion permet le calcul du remplissage en air sur une plage étendue de régimes. L'évolution à plusieurs cylindres est envisagée par la construction de matrices d'impédance.The pressure wave generated by the moving of the piston during the intake stroke of an internal combustion engine propagates in the duct carrying cool gases and comes back to the cylinder by reflections. Acoustic phenomena can increase the amount of air trapped in the engine by 30% and so its performances. Acoustic propagation in ducts carrying a turbulent flow is modelled in one and three dimensions. The input impedance is calculated and compared to the results of a new measurement procedure with steady flows up to Mach number M=0.15. A new method for measuring transfer matrices without flow has also been developed. Its results agree well with theory. The effect of acoustic properties of intake systems in the amount of air trapped in a one cylinder engine is modelled as a non-linear coupling of the combustion chamber with the input impedance, by a mechanical analogy. The acoustic pressures computed agree fairly well with the pressures measured in two different intake systems of a one-cylinder cold engine. The link between the acoustic properties of the intake duct expressed in the frequency domain alone and the volumetric efficiency of a cylinder has been quantified on a large range of running speed for the first time. In a multi-cylinder engine, the timing difference between intake strokes produces interferences in the intake system. The calculated impedance matrix and the study of phase explain a performance difference between cylinders that occurs in a turbocharged engine

Effects of the 2008-09 economic crisis on labor markets in Mexico

The 2008-09 economic crisis has had a long-lasting negative impact on the Mexican economy. This paper examines labor market dynamics in Mexico in light of the crisis. The labor market has been characterized in recent years by low relative unemployment, but high levels of informal jobs, low-growth, and almost stagnant real wages. In this context, the crisis destroyed a wide number of formal jobs, and even informal, increasing the unemployment rates to pre-crisis levels. Manufacturing was the sector that endured the largest job losses during the crisis and wages decreased for all sectors. The government of Mexico implemented a variety of programs to cope with the crises. However, these measures were too limited to counteract the large negative impact of the crisis on labor markets.Labor Markets,Labor Policies,Population Policies,Labor Standards,Economic Theory&Research

Economic progress of Porto Rico

Thesis (M.B.A.)--Boston University, 1931. This item was digitized by the Internet Archive

Distributed Cognitive RAT Selection in 5G Heterogeneous Networks: A Machine Learning Approach

The leading role of the HetNet (Heterogeneous Networks) strategy as the key Radio Access Network (RAN) architecture for future 5G networks poses serious challenges to the current cell selection mechanisms used in cellular networks. The max-SINR algorithm, although effective historically for performing the most essential networking function of wireless networks, is inefficient at best and obsolete at worst in 5G HetNets. The foreseen embarrassment of riches and diversified propagation characteristics of network attachment points spanning multiple Radio Access Technologies (RAT) requires novel and creative context-aware system designs. The association and routing decisions, in the context of single-RAT or multi-RAT connections, need to be optimized to efficiently exploit the benefits of the architecture. However, the high computational complexity required for multi-parametric optimization of utility functions, the difficulty of modeling and solving Markov Decision Processes, the lack of guarantees of stability of Game Theory algorithms, and the rigidness of simpler methods like Cell Range Expansion and operator policies managed by the Access Network Discovery and Selection Function (ANDSF), makes neither of these state-of-the-art approaches a favorite. This Thesis proposes a framework that relies on Machine Learning techniques at the terminal device-level for Cognitive RAT Selection. The use of cognition allows the terminal device to learn both a multi-parametric state model and effective decision policies, based on the experience of the device itself. This implies that a terminal, after observing its environment during a learning period, may formulate a system characterization and optimize its own association decisions without any external intervention. In our proposal, this is achieved through clustering of appropriately defined feature vectors for building a system state model, supervised classification to obtain the current system state, and reinforcement learning for learning good policies. This Thesis describes the above framework in detail and recommends adaptations based on the experimentation with the X-means, k-Nearest Neighbors, and Q-learning algorithms, the building blocks of the solution. The network performance of the proposed framework is evaluated in a multi-agent environment implemented in MATLAB where it is compared with alternative RAT selection mechanisms

A new Variable Curvature concept for Linear Fresnel Reflectors Solar Concentrating Systems

In a Linear Fresnel Reflector (LFR) solar concentrating system [1] a series of single axis linear reflectors target the sunrays to a longitudinal facedown receiver on top of a fixed structure. The LFR technology offers simplicity and reduced costs when compared with the standard Parabolic Trough technology, but it also suffers from reduced optical performance, especially with large incidence angles. The present preliminary study explores the possibilities of a variable curvature geometrical concept for a LFR that would achieve a more focused solar print over the receptor than in a traditional fixed geometry system.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

“Voces y espejos” de Espido Freire. Hacia una estética de la perversión en el relato especular

Espido Freire (Bilbao, 1974) is one of the most interesting authors of contemporary Spanish literature. She has admitted on numerous occasions her preference for tales. “Voces y espejos” belonging to the storybook Juegos míos (2004), is offered as a paradigm of the obsessions that populate her work: the voices and mirrors as inducers of evil. The mise en abyme while splitting the narrator – widely studied by Lucien Dällenbach – permits the author to develop an alter ego what was so beloved by Borges and Cortázar. And here it aims at a hidden voice in us, which is subtle, barely perceptible, but always evil, which is intended to be reflected by the mirror dangerously. This story also presents the particularity of applying a double mise en abyme for its metaliterary character, what refers to the proper conception and reception of the story in a macabre triangle between the author, text and reader