An integrative approach for modeling and simulation of Heterocyst pattern formation in Cyanobacteria strands

A comprehensive approach to cellular differentiation in cyanobacteria is developed. To this aim, the process of heterocyst cell formation is studied under a systems biology point of view. By relying on statistical physics techniques, we translate the essential ingredients and mechanisms of the genetic circuit into a set of differential equations that describes the continuous time evolution of combined nitrogen, PatS, HetR and NtcA concentrations. The detailed analysis of these equations gives insight into the single cell dynamics. On the other hand, the inclusion of diffusion and noisy conditions allows simulating the formation of heterocysts patterns in cyanobacteria strains. The time evolution of relevant component concentrations are calculated allowing for a comparison with experiments. Finally, we discuss the validity and the possible improvements of the model.Comment: 20 pages (including the supporting information), 8 figure

An eMath Teacher TOOL for ACTIVE LEARNING FLEURY'S ALGORITHM

An eMathTeacher [Sánchez-Torrubia 2007a] is an eLearning on line self assessment tool that help students to active learning math algorithms by themselves, correcting their mistakes and providing them with clues to find the right solution. The tool presented in this paper is an example of this new concept on Computer Aided Instruction (CAI) resources and has been implemented as a Java applet and designed as an auxiliary instrument for both classroom teaching and individual practicing of Fleury’s algorithm. This tool, included within a set of eMathTeacher tools, has been designed as educational complement of Graph Algorithm active learning for first course students. Its characteristics of visualization, simplicity and interactivity, make this tutorial a great value pedagogical instrument

Optimising airline maintenance scheduling decisions

Airline maintenance scheduling (AMS) studies how plans or schedules are constructed to ensure that a fleet is efficiently maintained and that airline operational demands are met. Additionally, such schedules must take into consideration the different regulations airlines are subject to, while minimising maintenance costs. In this thesis, we study different formulations, solution methods, and modelling considerations, for the AMS and related problems to propose two main contributions. First, we present a new type of multi-objective mixed integer linear programming formulation which challenges traditional time discretisation. Employing the concept of time intervals, we efficiently model the airline maintenance scheduling problem with tail assignment considerations. With a focus on workshop resource allocation and individual aircraft flight operations, and the use of a custom iterative algorithm, we solve large and long-term real-world instances (16000 flights, 529 aircraft, 8 maintenance workshops) in reasonable computational time. Moreover, we provide evidence to suggest, that our framework provides near-optimal solutions, and that inter-airline cooperation is beneficial for workshops. Second, we propose a new hybrid solution procedure to solve the aircraft recovery problem. Here, we study how to re-schedule flights and re-assign aircraft to these, to resume airline operations after an unforeseen disruption. We do so while taking operational restrictions into account. Specifically, restrictions on aircraft, maintenance, crew duty, and passenger delay are accounted for. The flexibility of the approach allows for further operational restrictions to be easily introduced. The hybrid solution procedure involves the combination of column generation with learning-based hyperheuristics. The latter, adaptively selects exact or metaheuristic algorithms to generate columns. The five different algorithms implemented, two of which we developed, were collected and released as a Python package (Torres Sanchez, 2020). Findings suggest that the framework produces fast and insightful recovery solutions

Factores de calidad del servicio en el transporte público de pasajeros: estudio de caso de la ciudad de Toluca, México

En este artículo se identifican, ponderan y valoran los factores que intervienen en la percepción de la calidad de servicio del transporte público en un corredor urbano que se caracteriza por una gestión delegada con tarifa fija y competencia en calidad. Mediante un modelo logit con especificación lineal de la función de utilidad, se estiman los coeficientes de cada factor de calidad de servicio para diferentes segmentos y estratos de la población. Los resultados de la estimación econométrica determinan la importancia, peso y valor de cada factor en términos de utilidad. De esta manera se obtiene que los factores principales que determinan la calidad del servicio son: el estado físico de los autobuses, la forma de manejo del conductor, la tarifa (costo del viaje), el tiempo que está dentro del autobús (tiempo de viaje) y el trato al usuario

Balance and characteristics of job market and employment generation in Colombia 2002-2010

Este artículo presenta un balance enmateria de empleo y mercado de trabajo en Colombia en el período 2002-2010, dando especial relevancia al trabajo informal, independiente y por cuenta propia, por su trascendencia en la reciente evolución¡ del mercado laboral. El estudio se enfoca en el análisis de las cifras de este mercado, que ofrece el Departamento Administrativo Nacional de Estadística DANE, y, a partir de los resultados, se plantea que los rasgos principales del desarrollo reciente del empleo en Colombia son su informalidad e independencia.This article presents a balance regarding employment and job market in Colombia from 2002 to 2010. Due to its significance in the recent evolution of labor market, special focus is given to informal, independent, and selfemployment work. The research is focused on the analysis of information of labor market of the National Administrative Department of Statistics (DANE, for its acronym in Spanish), and based on the results, it is said that informality and independence are the main characteristics of the recent development of employment in Colombia.Fil: Sanchez Torres, Roberto Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Centro de Estudios e Investigaciones Laborales; Argentin

Les approches, les concepts et les méthodologies pour mesurer le travail informel en Colombie

Este trabajo compara los principales enfoques conceptuales y empíricos sobre la informalidad laboral en Colombia. Estos enfoques generalmente se remiten a las discusiones conceptuales que se han desarrollado en América Latina, y aplican mediciones propias que discrepan en la unidad de análisis y en los criterios de identificación de la informalidad. Utilizando como fuente la Gran Encuesta Integrada de Hogares, se encuentra que la magnitud de la informalidad es diferente dependiendo del enfoque, teniendo un rango de 16 a 59%. Al comparar la metodología de medición de la informalidad laboral desde siete perspectivas, se encuentran diferencias en la magnitud de la informalidad, en su trayectoria reciente, en los individuos que se incluyen y en la influencia de algunos atributos socioeconómicos y ocupacionales sobre la probabilidad de ser trabajador informal.This paper compares the main conceptual and empirical approaches to labor informality in Colombia. These approaches generally take into account conceptual discussions developed in Latin America and present measures differing in the unit of analysis and informality identification criteria. Using data from the Large Integrated Household Survey, it is shown that the size of informality can be different depending on the methodological approach, with a rate ranging from 16 to 59%. When comparing seven methodological approaches to labor informality, disagreement is found regarding the magnitude of informality, its recent evolution, individuals included, and in the influence of socio-economic and occupational attributes on the probability of being an informal worker.Cet article établi des comparaisons entre les différentes approches conceptuelles et empiriques concernant l’étude de l’emploi informel en Colombie. Ces approches sont constituées par des discussions conceptuelles qui ont eu lieu en Amérique Latine, lesquelles proposent des différentes mesures pour l’emploi informel en établissant ainsi un désaccord sur analyse traditionnelle et sur l'identification des critères d'informalité. À partir de l'Enquête Intégrée des Ménages, nous montrons que l'ampleur de l'informalité dépend de l'approche théorique utilisée, dans un domaine qui va du 16% au 59%. En comparant la méthode de mesure de l’emploi informel dans sept approches différentes, nous trouvons des différences significatives dans l'ampleur de l'informalité, dans son évolution récente, chez les individus qui y sont considérés et dans l'influence de certains de leurs attributs socioéconomiques et professionnels sur la probabilité d'être travailleur informel.Fil: Sanchez Torres, Roberto Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Centro de Estudios E Investigaciones Laborales; Argentina. Universidad Nacional de Colombia; Colombi

Generation of heterogeneous cellular structures by sonication

Many materials require functionally graded cellular microstructures whose porosity (i.e. ratio of the void volume to the total volume of a material) is engineered to meet specific requirements and for an optimal performance in diverse applications. Numerous applications have demonstrated the potential of porous materials in areas ranging from biomaterial science through to structural engineering. Polymeric foams are an example of a cellular material whose microstructure can be considered as a blend of material and nonmaterial zones. While a huge variety of foams can be manufactured with homogenous porosity, for heterogeneous foams there are no generic processes for controlling the distribution of porosity throughout the resulting matrix. Motivated by the desire to create a flexible process for engineering heterogeneous foams, this work has investigated how ultrasound, applied during some of the foaming stages of a polyurethane melt, affects both the cellular structure and distribution of the pore size. After reviewing the literature concerning foam chemistry, ultrasound and sonochemistry, series of experiments were performed that used an ultrasonic field created by a sonotrode irradiating in a water bath containing a strategically placed vessel filled with foaming reactants. Prior to this, the acoustic field in the bath had been accurately mapped so that the acoustic pressure conditions within the foam container were known. During the foam polymerisation reaction, the acoustic pressure in the water bath varied causing the bubbles to pulsate in a state of ‘stable cavitation’ (i.e. rectified diffusion). This pulsation of the bubbles pumped gas from the liquid to the gas phase inducing them to increase in volume. The eventual solidification resulted in a porous material with a cellular structure that reflected the acoustic field imposed upon it. The experimental results revealed how the parameters of ultrasound exposure (i.e. frequency and acoustic pressure) influenced the volume and distribution of pores within the final polyurethane matrix: it was found that porosity varies in direct proportion to both the acoustic pressure and the frequency of the ultrasound signal. The effects of ultrasound on porosity demonstrated by this work offer the prospect of a manufacturing process that can control and adjust the cellular geometry of foam and hence ensure that the resulting characteristics of the heterogeneous material match the functional requirements.Engineering and Physical Sciences Research Council (EPSRC)Neilson Endowment Fund, in the Department of Mechanical Engineerin