167 research outputs found
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 sanguÃneo de alpacas, en la comunidad de Guangaje, cantón PujilÃ.
El presente trabajo se realizó en la comunidad de Guangaje del Cantón Pujilà 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 perÃodo 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 sanguÃneo 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 analÃtico – 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) varÃan con respecto al tipo de clima, a la altitud sobre el nivel del mar y al diferente tipo de alimentación en el suero sanguÃneo 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 sanguÃneo 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 sanguÃneo 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 caracterÃsticas 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 AndalucÃa. ConsejerÃa 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 AndalucÃa. ConsejerÃa 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 metodologÃa docente mediante el uso de la técnica de mapas conceptuales
El objetivo de este trabajo es desarrollar un método cientÃfico de diseño de una metodologÃa 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 estadÃsticas 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 metodologÃas
docentes que pueden servir de guÃa en la elaboración del programa de la asignatura, asà 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
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