Identification et modélisation du comportement des structures composites assemblées par cloutage

L'optimisation des structures aéronautiques fabriquées en composite a mené EADS-IW à développer une technique d’assemblage par cloutage qui a pour objectif la fabrication à coût réduit de sous ensembles structuraux avec un fort niveau d'intégration. L'objectif de ce travail de thèse est d'étudier le comportement mécanique des assemblages cloutés et de proposer des modélisations associées. Dans le cadre d'une démarche multi-niveau, le comportement des liaisons clou/résine et clou stratifié a d'abord été étudié. Des campagnes expérimentales ont montré l'influence du diamètre du clou et de la profondeur d'enfoncement sur la tenue en arrachement ainsi que des similitudes entre le comportement du clou noyé dans de la résine et implanté dans le stratifié. Une modélisation capable d'estimer la tenue en arrachement d'un clou a été développée. Au niveau éprouvettes technologiques, des éprouvettes cloutées représentatives de structures aéronautiques de type « L » ou « T » ont été testé en sollicitations statiques montrant l'influence des paramètres de conception et les possibles avantages du cloutage. Finalement, des modélisations basées sur les études élémentaires ont permis de simuler le comportement de ces éprouvettes cloutées retrouvé en essai et notamment de prédire leur tenue sous sollicitations différentes validant ainsi la démarche multi-niveau

Sampling rare trajectories using stochastic bridges

The numerical quantification of the statistics of rare events in stochastic processes is a challenging computational problem. We present a sampling method that constructs an ensemble of stochastic trajectories that are constrained to have fixed start and end points (so-called stochastic bridges). We then show that by carefully choosing a set of such bridges and assigning an appropriate statistical weight to each bridge, one can focus more processing power on the rare events of a target stochastic process while faithfully preserving the statistics of these rate trajectories. Further, we also compare the stochastic bridges produced using our method to the Wentzel-Kramers-Brillouin (WKB) optimal paths of the target process, derived in the limit of low noise. We see that the paths produced using our method, encoding the full statistics of the process, collapse onto the WKB optimal path as the level of noise is reduced. We propose that our method can be used to judge the accuracy of the WKB approximation at finite levels of noise

Determinación de macro y micro minerales en suero sanguíneo de alpacas, en la comunidad de Guangaje, cantón Pujilí.

El presente trabajo se realizó en la comunidad de Guangaje del Cantón Pujilí de la Provincia de Cotopaxi localizada a más de 3.600 m.s.n.m.., y en la Unidad Académica de Ciencias Agropecuarias y Recursos Naturales (CAREN) de la Universidad Técnica de Cotopaxi, durante el período de seis meses (abril – septiembre del 2011). Lapso en el cual se realizó el trabajo de campo, análisis de laboratorio y desarrollo investigativo de 26 muestras de suero sanguíneo de alpacas para determinar la cantidad de macro y microminerales (calcio, fósforo, magnesio y sodio, potasio, cloro). Este estudio se realizó utilizando el diseño metodológico analítico – descriptivo por lo tanto se pretende presentar los valores reales de los niveles de minerales en la sangre de las alpacas por medio de la investigación de campo y laboratorio. Su importancia radica principalmente en conocer si los niveles de minerales (macro – micro) varían con respecto al tipo de clima, a la altitud sobre el nivel del mar y al diferente tipo de alimentación en el suero sanguíneo de las alpacas ya que, existen pocos estudios con respecto a los camélidos sudamericanos y sobre todo a la determinación de componentes minerales en fluido sanguíneo de alpacas. Se desarrolló un muestreo en estos dos lugares con diferente tipo de alimentación y altitud para por medio de la técnica de extracción de sangre intravenosa y el análisis de laboratorio de suero sanguíneo se identificó cada una de las cantidades de macro y microminerales (calcio, fósforo, magnesio y sodio, potasio, cloro)

Fundamentos, estructura y programación de los procesadores digitales de señal. Familia TMS320C3X de Texas Instruments.

El Congreso TAEE'04, organizado por la Universidad Politécnica de Valencia, tuvo lugar entre el 14 de julio y el 17 de Julio de 2004.Este trabajo resume y presenta las principales características y contenido de una nueva obra, recientemente publicada, relacionada con el procesador digital de señal (DSP) TMS320C3x de Texas Instruments. La obra se centra en ofrecer aplicaciones prácticas basadas en los DSPs comentados, abordándose la labor de diseño de un sistema digital completo y mitigando el déficit que existe en cuanto a este tipo de material lectivo y educativo

Endemic infectious states below the epidemic threshold and beyond herd immunity

In the recent COVID-19 pandemic we assisted at a sequence of epidemic waves intertwined by anomalous fade-outs with periods of low but persistent epidemic prevalence. These long-living epidemic states complicate epidemic control and challenge current modeling approaches as classical epidemic models fail to explain their emergence. Inspired by this phenomenon, we propose a simple mechanism able to reproduce several features observed in real data. Specifically, here we introduce a modification of the Susceptible-Infected-Recovered (SIR) model in a meta-population framework where a small inflow of infected individuals accounts for undetected internal or imported cases. Focusing on a regime where this external seeding is so small that cannot be detected from the analysis of epidemic curves, we find that outbreaks of finite duration percolate in time resulting in overall low but long-living epidemic states below and above the epidemic threshold. Using a two-state description of the local dynamics, we can extract analytical predictions for the phase space. The comparison with epidemic data demonstrates that our model is able to reproduce some critical signatures observed in COVID-19 spreading in England. Finally, our findings defy our understanding of the concept of epidemic threshold and its relationship with outbreaks survival for disease control.Comment: Corrected typo

Squeezing resulting from a fourth-order interaction in a degenerate parametric amplifier with absorption losses

7 págs.; 8 figs.The squeezing properties of a model of a degenerate parametric amplifier with absorption losses and an added fourth-order nonlinearity have been analyzed. The approach used consists of obtaining the Langevin equation for the optical field from the Heisenberg equation provided that a linearization procedure is valid. The steady states of the deterministic equations have been obtained and their local stability has been analyzed. The stationary covariance matrix has been calculated below and above threshold. Below threshold, a squeezed vacuum state is obtained and the nonlinear effects in the fluctuations have been taken into account by a Gaussian decoupling. In the case above threshold, a phase-squeezed coherent state is obtained and numerical simulations allowed to compute the time interval, depending on the loss parameter, on which the system jumps from one stable state to the other. Finally, the variances numerically determined have been compared with those obtained from the linearized theory and the limits of validity of the linear theory have been analyzed. It has become clear that the nonlinear contribution may perhaps be profitably used for the construction of above-threshold squeezing devices. © 1991 The American Physical Society.Peer Reviewe

An empirical study of the driving forces behind online communities

Purpose – A large variety of online communities have emerged during the last years as a result of the challenges faced by both the business and scientific worlds. This trend has also been promoted by the development of internet and new Web 2.0 technologies. In this context, this paper is focused on the determinants of success of online communities. But, as a difference from other studies, these determinants are analyzed from the social network analysis perspective. Several constructs related to the community organization as a social network are proposed and their interrelations are hypothesized in a general research framework. The obtained results test the proposed model providing the most relevant antecedents of the project success. Design/methodology/approach – A case study based on Linux ports to non-conventional processor and environments is used to test the proposed model. Structural equation modeling analysis is used to validate the structural proposed model. Findings – The main antecedents of online communities’ success, quantifying the strength of the relation through the standardized path coefficients. Research limitations/implications – The research is limited to a particular set of online communities engaged with the development of the non-conventional Linux ports. However, they constitute a representative set of communities in the field of the open source projects (OSS) development, which are typically developed using a community of support. Originality/value – This paper fulfils the main antecedents causing the successful development of Internet virtual communities. Instead of using sources of data coming from users’ surveys, this study employs community interactions as a source of data. Results have important implications over the development of online communities, like software business models based on virtual communities and open source softwareMinisterio de Educación y Ciencia DPI2007-60128Junta de Andalucía. Consejería de Innovación, Ciencia y Empresa P07-TIC-0262

The role of Internet in the development of future software projects

Purpose – The Internet has evolved, prompted in part by new Web 2.0 technologies, to become a more widespread platform for interaction, communication, and activism. Virtual communities, or groups of people informally bound together by shared expertise, synthesise this Internet evolution and theWeb 2.0 technology. Users increasingly want to engage online with one another and with organisations of all kinds. These novel Internet-based technologies dominate the new business models of the digital economy giving companies radical new ways to harvest the talents of innovators working outside corporate boundaries. One of the most illustrative examples of this new trend is the Open Source Software (OSS) projects development. This paper aims to analyse the structure and topology of the virtual community supporting one of the most successfully OSS projects, Linux. The objective is to provide conclusions for being successful in the development of future virtual communities. As companies learn to manage these virtual communities, they will develop smarter and faster ways to create value through them. Design/methodology/approach – The interactions of the virtual community members of an ARM-embedded Linux project website is analysed through social network analysis techniques. The participants’ activity is studied and some conclusions about the participation features are obtained using the Gini coefficient. In particular, a participation inequality behaviour or a concentration on a small number of developers is clearly observed. Findings – The paper deals with the guidelines that virtual communities should follow to be successful. Results about the structure of a successful virtual community and its time evolution are provided to determine the mentioned guidelines. Research limitations/implications – The research is limited to a particular virtual community engaged with the development of the ARM-embedded Linux OSS. Other successful virtual communities can be analysed, and the conclusions could be compared. Anyway, the proposed analysis methodology can be extended to other virtual communities. Originality/value – The paper fulfils the development and features of Internet virtual communities to be successful. Results have important implications over the development of new software business models based on virtual communities and open source software. Contributions about the best organisation of virtual communities leading to a successful development of the underlying project are presented.Ministerio de Educación y Ciencia DPI2007- 60128Junta de Andalucía. Consejería de Innovación, Ciencia y Empresa P07-TIC-0262

Implementation of a web-based educational tool for digital signal processing teaching using the technological acceptance model

This paper presents an exploratory study about the improvement and validation of a Web-based educational tool. The tool, designed with Shockwave and Macromedia Director, is used as a teaching methodology in an undergraduate course using modern microprocessors, architectures, and applications. An information system theory, called the Technological Acceptance Model (TAM), has been applied to detect both the use of the tool and the external variables that have a significant influence over it. The obtained results illustrate the strengths and weaknesses to be reinforced and have been taken into account to implement the final version of the tool. The proposed method may be extended to similar tools and experiments to fill the lack of scientific studies in the validation and acceptance of computer-based educational tool

Diseño de una metodología docente mediante el uso de la técnica de mapas conceptuales

El objetivo de este trabajo es desarrollar un método científico de diseño de una metodología docente y su aplicación práctica a una asignatura relacionada con la enseñanza de los procesadores digitales de señal. El método propuesto se basa en la técnica de los mapas conceptuales, que hace uso de técnicas estadísticas multivariantes para sistematizar el conocimiento y experiencia de docentes relacionados con la enseñanza de esta asignatura. Como resultado del estudio se obtiene un conjunto de metodologías docentes que pueden servir de guía en la elaboración del programa de la asignatura, así como la importancia relativa de los contenidos incluidos en ellas. La fiabilidad del método es comparada con otros estudios similares y los resultados analizados en las conclusiones finale