Electrodispersion of a liquid of finite elcetrical conductivity in an immiscible dielectric liquid

Order-of-magnitude estimates and numerical computations are used to analyze an electrospray operating in the cone-jet mode in a bath of an immiscible dielectric liquid. In agreement with experimental results in the literature, the analysis predicts that the electric current carried by the jet increases as the square root of the flow rate of dispersed liquid in a wide range of conditions of the flow. The characteristics of the current transfer region determining the electric current are estimated taking into account the viscous drag of the dielectric liquid that surrounds the jet. The electric current is predicted to depart from the square root law for small flow rates, when charge relaxation effects become important in the current transfer region, and also when the flow rate increases to values of the order of QM = ϵ0γ2a/μ22K, where ϵ0 and μ2 are the permittivity and viscosity of the dielectric liquid, K is the electrical conductivity of the dispersed liquid, a is the radius of the capillary needle through which this liquid is injected, and γ is the interfacial tension of the liquid pair. When the flow rate becomes of order QM, the meniscus at the tip of the capillary ceases to resemble a Taylor cone, the current transfer region ceases to be short compared to the size of the meniscus, the electric current levels to a constant value, and the stationary jet cannot extend very far downstream of the meniscus

Effects of fresh gas velocity and thermal expansion on the structure of a Bunsen flame tip

Numerical computations and order-of-magnitude estimates are used to describe the tip region of a Bunsen flame where the flame departs from a planar flame at an angle to the incoming fresh gas flow. A single irreversible Arrhenius reaction with high activation energy is assumed. The well-known linear relation between flame velocity and curvature is recovered in the thermodiffusive limit, when the thermal expansion of the gas is left out, for velocities of the fresh gas (U0) only slightly larger than the velocity of a planar flame (UL), provided this flame is stable. For large values of the velocity ratio U0/UL, the tip region becomes slender and the curvature of the reaction sheet at the tip increases proportionally to U0/UL. The thermal expansion of the gas across the flame reduces the aspect ratio of the tip region. A qualitative analysis of the structure of the tip region for very exothermic reactions shows that this region ceases to be slender when the burnt-to-fresh gas temperature ratio becomes of the order of the velocity ratio U0/UL. For even larger values of the temperature ratio, the tip region becomes a cap of characteristic size not very different from the thickness of a planar flam

Numerical computation of the domain of operation of an electrospray of a very viscous liquid

A numerical study is carried out of the injection of a very viscous liquid of small electrical conductivity at a constant flow rate through an orifice in a metallic plate under the action of an electric field. The conditions under which the injected liquid can form an elongated meniscus with a thin jet emanating from its tip are investigated by computing the flow, the electric field and the transport of electric charge in the meniscus and a leading region of the jet. A stationary solution is found only for values of the flow rate above a certain minimum. At moderate values of the applied field, this minimum flow rate decreases when the applied field or the conductivity of the liquid increase. The electric shear stress acting on the surface of the liquid is not able to drive the liquid into the jet at flow rates smaller than the minimum while, for any flow rate higher than the minimum, the transfer of electric current to the surface may occur in a slender region of the jet where charge relaxation effects are small and the field induced by the electric charge of the jet is important. At high values of the applied field, the flow rate must be higher than another minimum, which increases with the applied field, in order for the viscous stress to balance the strong electric stress acting on the meniscus. The two conditions taken together determine lower and upper bounds for the applied field at a given flow rate, but the value of the applied field at which a stationary jet is first established when this parameter is gradually increased is higher than the lower bound, leading to hysteresis. When the liquid is electrosprayed in a surrounding dielectric fluid, the viscous shear stress that this fluid exerts on the surface of the jet eventually balances the electric shear stress and stops the continuous stretching of the jet. A fraction of the conduction current is left in the jet when the effect of the outer liquid comes into play in the region where this current is transferred to the surface, and no stationary solution is found above a maximum flow rate that decreases when the viscosity of the outer liquid increases or the applied field decreases. Order of magnitude estimates of the electric current and the conditions in the current transfer region are worked out

A short curriculum of the robotics and technology of computer lab

Our research Lab is directed by Prof. Anton Civit. It is an interdisciplinary group of 23 researchers that carry out their teaching and researching labor at the Escuela Politécnica Superior (Higher Polytechnic School) and the Escuela de Ingeniería Informática (Computer Engineering School). The main research fields are: a) Industrial and mobile Robotics, b) Neuro-inspired processing using electronic spikes, c) Embedded and real-time systems, d) Parallel and massive processing computer architecture, d) Information Technologies for rehabilitation, handicapped and elder people, e) Web accessibility and usability In this paper, the Lab history is presented and its main publications and research projects over the last few years are summarized.Nuestro grupo de investigación está liderado por el profesor Civit. Somos un grupo multidisciplinar de 23 investigadores que realizan su labor docente e investigadora en la Escuela Politécnica Superior y en Escuela de Ingeniería Informática. Las principales líneas de investigaciones son: a) Robótica industrial y móvil. b) Procesamiento neuro-inspirado basado en pulsos electrónicos. c) Sistemas empotrados y de tiempo real. d) Arquitecturas paralelas y de procesamiento masivo. e) Tecnología de la información aplicada a la discapacidad, rehabilitación y a las personas mayores. f) Usabilidad y accesibilidad Web. En este artículo se reseña la historia del grupo y se resumen las principales publicaciones y proyectos que ha conseguido en los últimos años

On the microeconomic ingredients of competitiveness: efficiency, competition and differentiation

En este papel estudiamos los ingredientes principales que se consideran generalmente bajo concepto de la competitividad: la eficacia conectó a los costes de producción, de competición como medida de comportamiento y de diferenciación de producto; también consideramos el papel de las economías de la escala incluso si se consideran generalmente como variable tecnológica que afecta todas las firmas simétricamente. Deseamos determinar los efectos de estos "ingredientes" o de las fuentes de la competitividad en las variables relevantes del mercado en el equilibrio: precios, salida y beneficios. Nos centramos en la perspectiva de las decisiones firmes individuales de los revestimientos sobre competitividad y estudiamos los efectos de un movimiento tan unilateral. El marco del análisis es un modelo general del oligopoly con asimetrías en eficacia, la competición y la diferenciación. Pues esperado la eficacia de aumento es siempre una buena estrategia para la firma. Al menos aumentando el grado de competición y/o de diferenciación no sea siempre buenas estrategias para las firmas.

Accounting for Output Fluctuations in Mexico.

During the last years, Mexico has registered relatively large output falls. The business cycle accounting method of Chari, Kehoe and McGrattan (2007) is applied to the two most recent recessions in Mexico (including the “Tequila crisis”) in order to understand what are the most important wedges driving output over the cycle and to evaluate to what extent such falls may be smoothed. First, it is found that efficiency and labor wedges may reasonably account for output fluctuations in each recession. Second, counterfactual exercises suggest that the elimination of distortions represented in terms of the efficiency wedge might result in output falls about one third of those observed in the data.Business cycle accounting, Tequila crisis, Total factor productivity, Mexico

List pricing and pure strategy outcomes in a Bertrand-Edgeworth duopoly

Non-existence of a pure strategy equilibrium in a Bertrand-Edgeworth duopoly model is analyzed. The standard model is modified to include a list pricing stage and a subsequent price discounting stage. Both firms first simultaneously choose a maximum list price and then decide to lower the price, or not, in a subsequent discounting stage. List pricing works as a credible commitment device that induces the pure strategy outcome. It is shown that for a general class of rationing rules there exists a sub-game perfect equilibrium that involves both firms playing pure strategies. This equilibrium payoff dominates any other sub-game perfect equilibrium of the game. Further unlike the dominant firm interpretation of a price leader, we show that the small firm may have incentives to commit to a low price and in this sense assume the role of a leader

Average Effective Tax Rates in Mexico

The paper estimates average effective tax rates on consumption, labor and capital income for Mexico, using the method of Mendoza et al. (1994) and related extensions, including two novel refinements. On average, it is found that consumption taxes are roughly between 7 and 14%, whereas labor and capital income taxes are between 8 and 12.5%, and 8.5 and 15%, respectively. Tax estimates are found to be consistent with predictions from theory in general, both for Mexico as well as for a sample of OECD countries.effective tax rates, consumption tax, factor income taxes, international tax policy

Análisis del Discurso mediante el modelo de Toulmin

Dotzenes Jornades de Foment de la Investigació de la FCHS (Any 2006-2007