Product Differentiation with Consumer Arbitrage

Also published as Working Paper DFAEII 2003-01spatial price discrimination, product differentiation, personal arbitrage

On the relation between the IR continuum and the active galactic nucleus in Seyfert galaxies

A sample of the brightest known Seyfert galaxies from the CfA sample is analyzed on the basis of ISO photometric and spectroscopic data. Regardless of the Seyfert type, the mid-IR continuum emission from these galaxies is found to be correlated with the coronal line emission arising in the nuclear active region. Conversely, the correlation degrades progressively when moving from the mid- to the far-IR emission, where it ends to vanish. It is concluded that the mid-IR emission is largely dominated by dust heated by processes associated with the active nucleus whereas the far-IR is a different component most probably unrelated with the active region. We suggest that the far-IR component is due to dust heated by the stellar population in the disks of these galaxies.Comment: 6 pages, 3 figures To be published in Astronomy and Astrophysic

Emulsifaction of waste cooking oils and fatty acid distillates as diesel engine fuel

The scope of this paper is to analyze the possibilities and feasibilities, as well as the main experimental results reported about the emulsification method applied to waste cooking oils and fatty acid distillates as diesel engine fuels, compared with other commonly used methods. These waste products are obtained in the refining oil industry, food industry and service sector from the frying process, mainly. However, they are a little used as feedstocks to produce biofuels and constitute a potential source of contamination. From the review of the state of arts, significant decreases in exhaust emissions of nitrogen oxides, cylinder pressure, as well as increases of the ignition delay, brake specific fuel consumption, hydrocarbon, smoke opacity, carbon monoxide, particulate matters to emulsified waste cooking oils and fatty acid distillates compared with diesel fuel are reported. In some experiments the emulsified waste cooking oils achieved better performance than neat fatty acid distillates, neat waste cooking oils and their derivates methyl esters

Assessment of mortar evolution in pig slurry by mechanical and ultrasonic measurements

This work presents the results obtained in a long-term experiment focused on the study of the evolution of cementitious materials immersed in pig slurry at real conditions. Cement mortars were made with four different cement types and immersed in pig slurry for 48 months. Furthermore, to separate pure hydration process from pig slurry effect, mortar samples were immersed in water for 12 months at laboratory conditions. Compressive strength, X-ray diffraction and ultrasonic measurements were made in all samples. Ultrasonic measurements were made from ultrasonic images obtained from automatic ultrasonic inspections. Use of ultrasonic images has allowed the extraction of information about the state of the studied materials. An empirical relationship between ultrasonic velocity and compressive strength has been obtained and the long-term effect of pig slurry on cementitious materials has been determined

Flux-cutting and flux-transport effects in type-II superconductor slabs in a parallel rotating magnetic field

The magnetic response of irreversible type-II superconductor slabs subjected to in-plane rotating magnetic field is investigated by applying the circular, elliptic, extended-elliptic, and rectangular flux-line-cutting critical-state models. Specifically, the models have been applied to explain experiments on a PbBi rotating disk in a fixed magnetic field ${\bm H}_a$, parallel to the flat surfaces. Here, we have exploited the equivalency of the experimental situation with that of a fixed disk under the action of a parallel magnetic field, rotating in the opposite sense. The effect of both the magnitude $H_a$ of the applied magnetic field and its angle of rotation $\alpha_s$ upon the magnetization of the superconductor sample is analyzed. When $H_a$ is smaller than the penetration field $H_P$, the magnetization components, parallel and perpendicular to ${\bm H_a}$, oscillate with increasing the rotation angle. On the other hand, if the magnitude of the applied field, $H_a$, is larger than $H_P$, both magnetization components become constant functions of $\alpha_s$ at large rotation angles. The evolution of the magnetic induction profiles inside the superconductor is also studied.Comment: 12 pages, 29 figure

Los problemas de Matemáticas en el curriculum de EGB (Ciclo medio) : un estudio cuantitativo/descriptivo desde el punto de vista de su potencial heurístico

Los problemas matemáticos en el plan de estudios para niños de 8-1 1 años se analizan desde diferentes puntos de vista relacionados con el proceso de resolución de problemas. El objetivo de este análisis es obtener información que nos permita mejorar tanto el plan de estudios como la formación de los docentes. Todos los problemas en los libros de texto de cuatro series han sido examinados. Se ha estudiado su distribución por cursos, temas y tipos (cuya resolución implica y un grado creciente de creatividad: se han estudiado "ejercicios de reconocimiento", "ejercicios algorítmicos", "problemas de aplicación", "problemas de búsqueda abierta" y "situaciones problemáticas". Además, se ha llevado a cabo la solución estándar para cada problema, lo que nos permite identificar las herramientas heurísticas implícitamente contenidas y analizar sus distribuciones sobre cursos y temas. Los resultados nos llevan a concluir que el plan de estudios no estimula la resolución creativa de problemas. Esto es especialmente evidente en la falta casi completa de situaciones problemáticas (porcentajes entre 0.2 y 4.05), el bajo porcentaje de problemas de búsqueda abierta y el alto porcentaje de ejercicios de reconocimiento. Algunas materias como "conjuntos y relaciones" y "formas planas" cuando se examinan en detalle demuestran ser especialmente ilustrativas del papel crucial que tiene la filosofía detrás del plan de estudios para causar resultados tan pobres. El porcentaje de problemas en el currículo que contiene herramientas heurísticas es bajo en casi todos los cursos (alrededor del 13%). Con respecto a las herramientas heurísticas identificadas ("caso especial", "submetas", "examinar posibilidades", 2 dibujar una imagen o un diagrama "y" prueba y error "), la hegemonía de" submetas "(casi 50%) muestra cómo y cuando se puede lograr la heurística de resolución de problemas

High School Teachers use of Dynamic Software to generate serendipitous mathematical relations

In this study, we document and analyse problem-solving approaches that high school teachers exhibited as a result of using dynamic software (Cabri-Geometry) to construct and examine geometric configurations. What type of questions do teachers pose and pursue while representing and exploring mathematical tasks or objects dynamically? To what extent their initial problem solving strategies are enhanced with the use of the tools? Results indicate that the use of the tool offered the participants the opportunity of constructing geometric configuration (formed by simple mathematical objects) that led them to identify and explore key mathematical relations

Velocity-sensorless tracking control and identification of switched-reluctance motors

International audienceWe present a solution to the speed sensorless control problem for switched-reluctance motors under parametric uncertainty. Our main results guarantee velocity tracking control for velocity references with constant reference acceleration under the assumption that the load torque, the rotor inertia, the resistance and inductances are unknown. Under a persistency of excitation condition on a function which depends only on reference trajectories, we guarantee uniform global asymptotic stability therefore, we establish conditions for the identification of the physical parameters of the system. Our theoretical findings are supported by illustrative simulation results

Exponential stabilization of switched-reluctance motors via speed-sensorless feedback

International audienceWe solve the control problem of switched-reluctance motors without velocity measurements. Our controller is composed of a loop in the mechanical dynamics which consists of a PI2 D controller and a "tracking" controller closing an inner loop with the stator currents dynamics. The PI2 D controller consists in a linear proportional derivative controller in which the measurement of velocities is replaced by approximate derivatives of angular position. Then a double integrator is added, composed of an integral of the angular position errors and a second integral correction term in function of the approximate derivative. We show global exponential stability and illustrate the performance of our controller in numerical simulations

Comparative analysis of spontaneous blinking and the corneal reflex

Ocular surface health, the cognitive status, psychological health or human neurological disorders, among others, can be assessed by studying eye blinking, which can be differentiated in spontaneous, reflex and voluntary. Its diagnostic potential has provided a great number of works that evaluate their characteristics and variations depending on the subject's condition (sex, tiredness, health, …). The objective of this study was to analyse the differences in blinking kinematics of spontaneous and reflex blinks, distinguishing between direct and consensual reflexes, using a self-developed, non-invasive and image processing-based method. A video-oculography system is proposed using an air jet driven by a syringe to induce reflex and a high-speed camera to record the blinking of both eyes. The light intensity diffused by the eye changes during blinking and peaks when the eyelid closes. Sixty-second sequences were recorded of 25 subjects blinking. Intensity curves were off-line fitted to an exponentially modified Gaussian (EMG) function, whose σ, μ and τ parameters were analysed. A two-way analysis of variance (ANOVA) of these parameters was conducted to test the influence of the subject, the eye and blink type. In the closing phase, direct and consensual corneal reflexes are faster than spontaneous blinking, but there was no significant difference between them, nor between right and left eyes. In the opening phase, the direct corneal reflex was the slowest and significant differences appeared between right and left eyes