Presentación [del Anuario de espacios urbanos, historia, cultura y diseño 2002]

Los artículos que se publican en este Anuario de Espacios Urbanos, Historia, Cultura, Diseño 2002, no sólo se refieren a ciudades de muy diversas latitudes, sino, además, a su análisis en diversas temporalidades. Algunos estudios no fueron elaborados por ciudadanos de las localidades que tratan, sino por visitantes interesados en ellas desde muy diversas perspectivas. De igual manera, los trabajos muestran intereses distintos en lo que respecta al problema por ¡ponderar: el espacio o sus actores. La dudad como objeto o sujeto de reflexión, la ciudad que se vive, la que se diseña, aquella imaginada y descrita, la aprehendida y apropiada, estas y otras miradas están presentes en los artículos que forman esta edición y ratifican su visión primigenia manifiesta desde el primer Anuario publicado en 1994- y la del Área de Espacios Urbanos que se encarga de su publicación: entender la ciudad como una entidad que no puede ser agotada con una sola lectura, ya que siempre existirá una enorme desproporción entre un espacio finito y la imaginación infinita del investigador que le permite interpretarlo desde muchísimos ángulos

Linear theory for the interaction of small-scale turbulence with overdriven detonation

To complement our previous analysis of interactions of large-scale turbulence with strong detonations, the corresponding theory of interactions of small-scale turbulence is presented here. Focusing most directly on the results of greatest interest, the ultimate long-time effects of high-frequency vortical and entropic disturbances on the burnt-gas flow, a normal-mode analysis is selected here, rather than the Laplace-transform approach. The interaction of the planar detonation with a monochromatic pattern of perturbations is addressed first, and then a Fourier superposition for two-dimensional and three-dimensional isotropic turbulent fields is employed to provide integral formulas for the amplification of the kinetic energy, enstrophy, and density fluctuations. Effects of the propagation Mach number and of the chemical heat release and the chemical reaction rate are identified, as well as the similarities and differences from the previous result for the thin-detonation (fast-reaction) limit.This work was supported by the U.S. AFOSR Grant No. FA9550-12-1-0138.Publicad

Diffusion-flame ignition by shock-wave impingement on a supersonic mixing layer

Ignition in a supersonic mixing layer interacting with an oblique shock wave is investigated analytically and numerically under conditions such that the post-shock flow remains supersonic. The study requires consideration of the structure of the post-shock ignition kernel that is found to exist around the point of maximum temperature, which may be located either near the edge of the mixing layer or in its interior, depending on the profiles of the fuel concentration, temperature and Mach number across the mixing layer. The ignition kernel displays a balance between the rates of chemical reaction and of post-shock flow expansion, including the acoustic interactions of the chemical heat release with the shock wave, leading to increased front curvature. The analysis, which adopts a one-step chemistry model with large activation energy, indicates that ignition develops as a fold bifurcation, the turning point in the diagram of the peak perturbation induced by the chemical reaction as a function of the Damköhler number providing the critical conditions for ignition. While an explicit formula for the critical Damköhler number for ignition is derived when ignition occurs in the interior of the mixing layer, under which condition the ignition kernel is narrow in the streamwise direction, numerical integration is required for determining ignition when it occurs at the edge, under which condition the kernel is no longer slender. Subsequent to ignition, for the Arrhenius chemistry addressed, the lead shock will rapidly be transformed into a thin detonation on the fuel side of the ignition kernel, and, under suitable conditions, a deflagration may extend far downstream, along with the diffusion flame that must separate the rich and lean reaction products. The results can be helpful in describing supersonic combustion for high-speed propulsion

Weak-shock interactions with transonic laminar mixing layers of fuels for high-speed propulsion

This paper extends to transonic mixing layers an analysis of Lighthill ("Reflection at a Laminar Boundary Layer of a Weak Steady Disturbance to a Supersonic Stream, Neglecting Viscosity and Heat Conduction," Quarterly Journal of Mechanics and Applied Mathematics, Vol. 54, No. 3, 1950, pp. 303-325.) on the interaction between weak shocks and laminar boundary layers. As in that work, the analysis is carried out under linear-inviscid assumptions for the perturbation field, with streamwise changes of the base flow neglected, as is appropriate given the slenderness of the mixing-layer flow. The steady-disturbance profile is determined by taking a Fourier transform along the longitudinal coordinate. Closed-form analytical functions for the pressure field are derived in the small- and large-wave-number limits, and vorticity disturbances are obtained as functions of the pressure perturbations. The analysis is particularized to ethylene&-air and hydrogen&-air mixing layers, for which the dynamics are of current interest for hypersonic propulsion. The results provide, in particular, the effective distance of upstream influence of the pressure perturbation in the subsonic stream. The resulting value, which scales with the thickness of the subsonic layer, is much smaller than the upstream influence distances encountered in boundary layers. This study may serve as a basis to understand shock-induced autoignition and flameholding phenomena in simplified versions of non-premixed supersonic-combustion problems.This work was supported by the U.S. Air Force Office of Scientific Research grants FA9550-12-1-0138 and FA9550-14-1-0219. We aregrateful to Amable Liñán for useful conversations at the early stages of this project

Assessment of Cardiorespiratory Fitness without Exercise in Elderly Men with Chronic Cardiovascular and Metabolic Diseases

Low cardiorespiratory (CRF) is associated with health problems in elderly people, especially cardiovascular and metabolic disease. However, physical limitations in this population frequently preclude the application of aerobic tests. We developed a model to estimate CRF without aerobic testing in older men with chronic cardiovascular and metabolic diseases. Subjects aged from 60 to 91 years were randomly assigned into validation (n = 67) and cross-validation (n = 29) groups. A hierarchical linear regression model included age, self-reported fitness, and handgrip strength normalized to body weight (R2 = 0.79; SEE = 1.1 METs). The PRESS (predicted residual sum of squares) statistics revealed minimal shrinkage in relation to the original model and that predicted by the model and actual CRF correlated well in the cross-validation group (r = 0.85). The area under curve (AUC) values suggested a good accuracy of the model to detect disability in the validation (0.876, 95% CI: 0.793–0.959) and cross-validation groups (0.826, 95% CI: 0.677–0.975). Our findings suggest that CRF can be reliably estimated without exercise test in unhealthy elderly men

Interaction of Oblique Shocks and Laminar Shear Layers

This paper examines the steady interaction of a shear layer separating two uniform supersonic streams of Mach numbers M1 and M2 with an oblique shock approaching from the faster stream at an incident angle sigmai sufficiently small for the postshock flow to remain supersonic everywhere. The development begins by considering the related problem of oblique-shock impingement on a supersonic vortex sheet of infinitesimal thickness, for which the region of existence of regular shock refractions with downstream supersonic flow is delineated in the parametric space (M1,M2,sigmai). The interaction region located about the impingement point, scaling with the shear-layer thickness, is described next by integrating the Euler equations in the postshock region, formulated in characteristic form, subject to the Rankine-Hugoniot jump conditions at the shock front. The results are used to investigate the accuracy and limitations of a simplified treatment, the so-called Moeckel-Chisnell approach, commonly employed for determining the shape of the shock wave in these scenarios, which does not account for the influence of the postshock flow. It is found that, although the Moeckel-Chisnell method predicts accurately the shape of the shock front as it evolves across the shear layer, it is unable to predict the final transition to the transmitted-shock solution, which occurs beyond the edge of the shear layer. The structure of the shear layer in the far field also is addressed here for the first time, with the objective being to lay the groundwork for future studies of shock-induced ignition in supersonic fuel-air mixing layers.The work of A. L. Sánchez and F. A. Williams was supported by the U.S. Air Force Office of Scientific Research grant FA9550-16-1-0443, and that of D. Martínez-Ruiz and C. Huete was supported by the Spanish Ministry of Science (ENE2015-65852-C2-2-R) and the Fundación Iberdrola España (BYNV-ua37crdy)

Optimized Method for Locating the Source of Voltage Sags

Short-Duration Voltage Variations (SDVVs) are the power quality disturbances (PQD) that mainly affect industrial systems, and are originated for various reasons, in particular short circuits over large areas, even those originating in remote points of the electrical system. The location problem aims to indicate the area or region or distance from the substation that is connected to the source causing the voltage sags, and is a fundamental task to ensure good power quality. One of the strategies used to determine the location of sources causing SDVVs and for an implementation of machine learning algorithms in modern distribution networks, called Smart Grids. Monitoring a Smart Grid plays a key role, however mostly it generates a large volume of data (Big Data) and as a result, multiple challenges arise due to the properties of this data such as volume, variety and velocity. This work presents an optimization through genetic algorithm to select meters which already exist in the Smart Grid, using a voltage sag location method in order to reduce the data obtained and analyzed throughout the localization process. Optimization was evaluated through a comparison with a non-optimized localization method, this comparison showed a difference between the hit rates of less than 1%