Sistema de ecuaciones diferenciales como modelos de problemas de redes eléctricas

En ingeniería, sobre todo en Telecomunicaciones y Electrónica, es una necesidad modelar problemas de circuitos, convirtiéndose esto en una herramienta invaluable. El estudio de las ecuaciones diferenciales propone estrategias que conducen a entender mejor la modelación por parte de los estudiantes. La construcción de la formulación matemática requiere de cierta habilidad, imaginación y evaluación objetiva. Compartimos el criterio de Judson (1997), que plantea lo importante de propiciar la transferencia de los conocimientos a situaciones relacionadas con la solución de problemas del ejercicio de su profesión. De ahí lo importante de enseñar ecuaciones diferenciales. En este trabajo expondremos la resolución de un problema sobre redes eléctricas, que se modela mediante sistemas de ecuaciones diferenciales. Se plantea una metodología para obtener el modelo que represente lo más fielmente la realidad, lo que propicia llegar de forma acertada a la respuesta deseada

Asistente matemático. Herramienta necesaria en la enseñanza de la matemática

En este trabajo se propone el uso de un Asistente Matemático en la carrera de Ciencias Técnicas. Se persigue que el uso de este asistente matemático conlleve a un perfeccionamiento dentro del proceso docente‐educativo, que ponga al estudiante como centro del mismo, a través del uso de métodos y técnicas participativas, donde el alumno se sienta inmerso en este desarrollo (Castañeda, 1998). La introducción del asistente matemático como herramienta de trabajo en la Disciplina Matemática actuará como un nuevo elemento Didáctico Integrador en las carreras de Ciencias Técnicas. El uso del asistente matemático se ha ido incrementando paulatinamente y actualmente se hace una necesidad como un elemento más dentro del proceso Enseñanza – Aprendizaje. (Castañeda, 2001)

Propuesta metodológica para la resolución de problemas de corrientes a través de sistemas de ecuaciones diferenciales lineales de primer orden utilizando valores y vectores propios

La resolución de problemas es un aspecto importante en el aprendizaje de la Matemática. Es esencial que se tracen estrategias de trabajo que garanticen de forma eficiente las posibilidades que tiene la Matemática en la formación del estudiante para conseguir resolver con éxito los problemas a que se enfrenta. Coincidimos con (Delgado,1998, p.69), cuando considera la resolución de problemas como una habilidad matemática y señala que resolver: es encontrar un método o vía de solución que conduzca a la solución de un problema. En el trabajo abordaremos una experiencia sobre la resolución de problemas de corrientes en las redes eléctricas que nos inducen a la solución de Sistemas de Ecuaciones Diferenciales Lineales(SED) utilizando el método matricial. Se propone una metodología para la solución de estos SED mediante los valores y vectores propios, auxiliándonos del Asistente Matemático DERIVE

Minimum age requirements and the role of the school choice set

Using several data sources from Chile, we study the impact of the size of the school choice set at the time of starting primary school. With that purpose, we exploit multiple cutoffs defining the minimum age at entry, which not only define when a student can start elementary school, but also the set of schools from which she/he can choose. Moreover, differences across municipalities in the composition of the schools according to these cutoffs allow us not only to account for municipality fixed factors (educational markets) but also for differences in the characteristics between schools choosing different deadlines. That is, we compare the difference in outcomes for children living in the same municipality around the different cutoffs with those for children in other municipalities that experience a different change in the available set of schools across cutoffs (double difference in RD). We show that a larger set of schools increases the probability of starting in a better school, measured by a non-high-stakes examination. Moreover, this quasi-experimental variation reveals an important reduction in the likelihood of dropping out and a reduction in the probability that a child would switch schools during her/his school life. Second, for a subsample of students who have completed high school, we observe that a larger school choice set at the start of primary school increases students' chances of taking the national examination required for higher education and the likelihood of being enrolled in college.We gratefully acknowledge financial support from Fondecyt (Grant 1130565). Cáceres-Delpiano gratefully acknowledges financial support from the Spanish Ministry of Education (Grant ECO2019-00419-001), the Spanish Ministry of Economy and Competitiveness (MDM 2014-0431) and the Comunidad de Madrid, SPAIN (Grant CAM-EPUC3M11). We thank MINEDUC, DEMRE and Agencia de Calidad de la Educación (Chile) for the access to the data used in this paper

Asymmetric amplification in amino acid sublimation involving racemic compound to conglomerate conversion

A straightforward unprecedented sublimation protocol that reveals both conversion of a racemic compound into a racemic conglomerate and subsequent enantioenrichment has been developed for the proteinogenic amino acid valine. The phenomenon has been observed in closed and open systems, providing insight into asymmetric amplification mechanisms under presumably prebiotic condition

MARRIAGE MARKETS, DIFFERENTIAL FECUNDITY AND SEARCH

It is commonly observed that over time and across societies, women tend to marry older men. The traditional explanation for this phenomenon is that wages increase with age and hence older men are more attractive in the marriage market. The model developed in Chapter 2 of this dissertation shows that a marriage market equilibrium where women marry earlier in life than men can be achieved without making any assumptions about the wage process or gender roles. The only driving force in this model is the asymmetry in fecundity horizons between men and women. When the model is calibrated with Census Data, the average age at first marriage and the pattern of the sex ratio of single men to single women over different age groups mimics the patterns observed in developed countries during the last decade. Chapter 3 extends the model in order to analyze assortative mating. In this case people belong to one of two groups and prefer to marry someone within the group. In this chapter it is shown that, given constant preferences, the limited horizon for searching for a mate affects the likelihood of intermarriage through ages, and the dynamic is different for men and women. Chapter 4 is an empirical study and uses 1970 and 1980 US Census data to study how the local sex ratios of single men to single women affect several aspects of the marriage market. Unlike earlier literature, this work also investigates other margins over which individuals can substitute in the marriage market -- specifically the choice of spouse's characteristics. These new results suggest that a shortage of single men leads women (and also men) to marry earlier. This suggests a more elastic response for women to a tight marriage market than the one for men. This is consistent with a marriage model where the search horizon for women is shorter than the one for men, as the one developed in the previous chapters. The results also suggest that an adverse change in the sex ratio can lead both men and women to marry outside of their own racial or educational group

Anteproyecto de un equipo I.Q.F.(Individual Quick Freezing) de una capacidad de un ton/hr de frambuesas.

151 p.La presente memoria trata del anteproyecto del diseño de un IQF de una capacidad de una 1 ton/h de frambuesas. La técnica de congelado rápido en IQF tiene como principio que el producto atraviese por medio de una cinta transportadora un túnel con alta resistencia térmica en donde existe una circulación de aire a alta velocidad y además se encuentra a una temperatura de alrededor de –30 ºC. Para disponer de bajas temperaturas en el interior del túnel es necesario diseñar un sistema de refrigeración con una potencia frigorífica acorde a los requerimientos de las cargas térmicas que afectan al sistema. La mayor carga de enfriamiento presente en dicho sistema, para obtener un producto congelado al termino del proceso con una temperatura de alrededor de –18 ºC, es la carga por producto. Esta representa alrededor de un 80% de la carga térmica total. La carga por generación interna de calor producida por los motores de los ventiladores de alta velocidad, es significativa, ya que es un 10% del aporte de calor total, el 10% restante tiene como origen: infiltraciones, carga latente y conducción por paredes y pisos. En términos económicos, el producir frambuesas congeladas con un IQF es rentable, realizándose la evaluación económica del anteproyecto, ya que el primer año retorna la inversión y se obtiene rentabilidad, siendo además más beneficioso para el inversionista comprar el equipo en el mercado nacional que importarlo, ya que es posible ahorrar según el presente estudio un 30% en la inversión inicial

Predicting the ecological status of rivers and streams under different climatic and socioeconomic scenarios using Bayesian Belief Networks

Freshwater systems have increasingly been subjected to a multitude of human pressures and the re-establishment of their ecological integrity is currently a major worldwide challenge. Expected future climate and socioeconomic changes will most probably further exacerbate such challenges. Modelling techniques may provide useful tools to help facing these demands, but their use is still limited within ecological quality assessment of water resources due to its technical complexity. We developed a Bayesian Belief Network (BBN) framework for modelling the ecological quality of rivers and streams in two European river basins located in two distinct European climatic regions: the Odense Fjord basin (Denmark) and the Sorraia basin (Portugal). This method enabled us to integrate different data sources into a single framework to model the effect of multiple stressors on several biological indicators of river water quality and, subsequently, on their ecological status. The BBN provided a simple interactive user interface with which we simulated combined climate and socioeconomic changes scenarios to assess their impacts on river ecological status. According to the resulting BBNs the scenarios demonstrated small impacts of climate and socioeconomic changes on the biological quality elements analysed. This yield a final ecological status similar to the baseline in the Odense case, and slightly worse in Sorraia. Since the present situation already depicts a high percentage of rivers and streams with moderate or worse ecological status in both basins, this means that many of them would not fulfil the Water Framework Directive target in the future. Results also showed that macrophytes and fish indices were mainly responsible for a non-desirable overall ecological status in Odense and Sorraia, respectively. The approach followed in this study is novel, since BBN modelling is used for the first time for assessing the ecological status of rivers and streams under future scenarios, using an ensemble of biological quality elements. An important advantage of this tool is that it may easily be updated with new knowledge on the nature of relationships already established in the BBN or even by introducing new causal links. By encompassing two case studies of very different characteristics, these BBN may be more easily adapted as decision-making tools for water management of other river basinsinfo:eu-repo/semantics/publishedVersio