916 resultados para Long memory stochastic process


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Este trabajo tiene como finalidad presentar los principales lineamientos de lo que constituye mi proyecto tesis de investigación de posgrado explicitando los objetivos generales y particulares que se buscan alcanzar. Asimismo, se presentan cuestiones referidas a los desafíos que plantea el trabajo con entrevistas y observaciones participantes, especialmente las que atañen prácticas de grupos tradicionalmente silenciados y relegados al olvido como son las comunidades indígenas de Argentina. La posibilidad de entablar vínculos estrechos con miembros de estas comunidades que permitan dar cuenta de las experiencias personales y colectivas, las memorias sociales compartidas, las herencias ancestrales y culturales, constituye el resultado de un trabajo sostenido en el largo plazo. En este caso, el desarrollo de ésta investigación se plantea como un proceso conjunto y participativo, fruto de una experiencia de extensión universitaria que permitió el acercamiento y vinculación con la comunidad kolla, Asociación Civil Warmikunamanta Antipak Sonqokuna. En consecuencia, se buscará abrir a la reflexión sobre la producción de saberes en ciencias sociales, especialmente en los estudios sobre sociedades indígenas del siglo XXI

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Este trabajo tiene como finalidad presentar los principales lineamientos de lo que constituye mi proyecto tesis de investigación de posgrado explicitando los objetivos generales y particulares que se buscan alcanzar. Asimismo, se presentan cuestiones referidas a los desafíos que plantea el trabajo con entrevistas y observaciones participantes, especialmente las que atañen prácticas de grupos tradicionalmente silenciados y relegados al olvido como son las comunidades indígenas de Argentina. La posibilidad de entablar vínculos estrechos con miembros de estas comunidades que permitan dar cuenta de las experiencias personales y colectivas, las memorias sociales compartidas, las herencias ancestrales y culturales, constituye el resultado de un trabajo sostenido en el largo plazo. En este caso, el desarrollo de ésta investigación se plantea como un proceso conjunto y participativo, fruto de una experiencia de extensión universitaria que permitió el acercamiento y vinculación con la comunidad kolla, Asociación Civil Warmikunamanta Antipak Sonqokuna. En consecuencia, se buscará abrir a la reflexión sobre la producción de saberes en ciencias sociales, especialmente en los estudios sobre sociedades indígenas del siglo XXI

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Este trabajo consiste en una reflexión en torno a la represión cultural desplegada por la última dictadura cívico-militar argentina. El caso del profesor de Letras Luis Oscar Pato Lacoste, secuestrado y desaparecido en octubre de 1976, sirve de ejemplo para abordar la profundidad de la represión dictatorial en el plano cultural como un plan sistemático para la reestructuración y disciplinamiento social como fin último. La recuperación de este caso para la comunidad de Lobos viene de la mano de jóvenes estudiantes y es desde este lugar donde se va a abordar la construcción de la historia reciente y la memoria histórica local. La desaparición de Pato es entendida en un doble plano: la física- corporal y la cultural- representacional. Se cree asimismo importante la construcción y el aporte juvenil a la memoria de la comunidad de un proceso traumático aún no cerrado hoy en tanto impune, derribando el 'acá no ha pasado nada' ó el 'de eso no se habla'.

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Este trabajo consiste en una reflexión en torno a la represión cultural desplegada por la última dictadura cívico-militar argentina. El caso del profesor de Letras Luis Oscar Pato Lacoste, secuestrado y desaparecido en octubre de 1976, sirve de ejemplo para abordar la profundidad de la represión dictatorial en el plano cultural como un plan sistemático para la reestructuración y disciplinamiento social como fin último. La recuperación de este caso para la comunidad de Lobos viene de la mano de jóvenes estudiantes y es desde este lugar donde se va a abordar la construcción de la historia reciente y la memoria histórica local. La desaparición de Pato es entendida en un doble plano: la física- corporal y la cultural- representacional. Se cree asimismo importante la construcción y el aporte juvenil a la memoria de la comunidad de un proceso traumático aún no cerrado hoy en tanto impune, derribando el 'acá no ha pasado nada' ó el 'de eso no se habla'.

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Increasing pCO2 (partial pressure of CO2 ) in an "acidified" ocean will affect phytoplankton community structure, but manipulation experiments with assemblages briefly acclimated to simulated future conditions may not accurately predict the long-term evolutionary shifts that could affect inter-specific competitive success. We assessed community structure changes in a natural mixed dinoflagellate bloom incubated at three pCO2 levels (230, 433, and 765 ppm) in a short-term experiment (2 weeks). The four dominant species were then isolated from each treatment into clonal cultures, and maintained at all three pCO2 levels for approximately 1 year. Periodically (4, 8, and 12 months), these pCO2 -conditioned clones were recombined into artificial communities, and allowed to compete at their conditioning pCO2 level or at higher and lower levels. The dominant species in these artificial communities of CO2 -conditioned clones differed from those in the original short-term experiment, but individual species relative abundance trends across pCO2 treatments were often similar. Specific growth rates showed no strong evidence for fitness increases attributable to conditioning pCO2 level. Although pCO2 significantly structured our experimental communities, conditioning time and biotic interactions like mixotrophy also had major roles in determining competitive outcomes. New methods of carrying out extended mixed species experiments are needed to accurately predict future long-term phytoplankton community responses to changing pCO2 .

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We examined the long-term effect of naturally acidified water on a Cymodocea nodosa meadow growing at a shallow volcanic CO2 vent in Vulcano Island (Italy). Seagrass and adjacent unvegetated habitats growing at a low pH station (pH = 7.65 ± 0.02) were compared with corresponding habitats at a control station (pH = 8.01 ± 0.01). Density and biomass showed a clear decreasing trend at the low pH station and the below- to above-ground biomass ratio was more than 10 times lower compared to the control. C content and delta 13C of leaves and epiphytes were significantly lower at the low pH station. Photosynthetic activity of C. nodosa was stimulated by low pH as seen by the significant increase in Chla content of leaves, maximum electron transport rate and compensation irradiance. Seagrass community metabolism was intense at the low pH station, with significantly higher net community production, respiration and gross primary production than the control community, whereas metabolism of the unvegetated community did not differ between stations. Productivity was promoted by the low pH, but this was not translated into biomass, probably due to nutrient limitation, grazing or poor environmental conditions. The results indicate that seagrass response in naturally acidified conditions is dependable upon species and geochemical characteristics of the site and highlight the need for a better understanding of complex interactions in these environments.

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Recent evolution experiments have revealed that marine phytoplankton may adapt to global change, for example to ocean warming or acidification. Long-term adaptation to novel environments is a dynamic process and phenotypic change can take place thousands of generations after exposure to novel conditions. Using the longest evolution experiment performed in any marine species to date (4 yrs, = 2100 generations), we show that in the coccolithophore Emiliania huxleyi, long-term adaptation to ocean acidification is complex and initial phenotypic responses may revert for important traits. While fitness increased continuously, calcification was restored within the first 500 generations but later reduced in response to selection, enhancing physiological declines of calcification in response to ocean acidification. Interestingly, calcification was not constitutively reduced but revealed rates similar to control treatments when transferred back to present-day CO2 conditions. Growth rate increased with time in controls and adaptation treatments, although the effect size of adaptation assessed through reciprocal assay experiments varied. Several trait changes were associated with selection for higher cell division rates under laboratory conditions, such as reduced cell size and lower particulate organic carbon content per cell. Our results show that phytoplankton may evolve phenotypic plasticity that can affect biogeochemically important traits, such as calcification, in an unforeseen way under future ocean conditions.

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Ocean acidification, a process caused by the continuous rise of atmospheric CO2 levels, is expected to have a profound impact on marine invertebrates. Findings of the numerous studies conducted in this field indicate high variability in species responses to future ocean conditions. This study aimed at understanding the effects of long-term exposure to elevated pCO2 conditions on the performance of adult Echinometra sp. EE from the Gulf of Aqaba (Red Sea). During an 11-month incubation under high pCO2 (1,433 µatm, pHNBS 7.7) and control (435 µatm, pHNBS 8.1) conditions, we examined the urchins' somatic and gonadal growth, gametogenesis and skeletal microstructure. Somatic and gonadal growths were exhibited with no significant differences between the treatments. In addition, all urchins in the experiment completed a full reproductive cycle, typical of natural populations, with no detectable impact of increased pCO2 on the timing, duration or progression of the cycle. Furthermore, scanning electron microscopy imaging of urchin tests and spines revealed no signs of the usual observed effects of acidosis, such as skeletal dissolution, widened stereom pores or non-smoothed structures. Our results, which yielded no significant impact of the high pCO2 treatment on any of the examined processes in the urchins studied, suggest high resistance of adult Echinometra sp. EE to near future ocean acidification conditions. With respect to other findings in this area, the outcome of this study provides an example of the complicated and diverse responses of echinoids to the predicted environmental changes.

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Ocean acidification and greenhouse warming will interactively influence competitive success of key phytoplankton groups such as diatoms, but how long-term responses to global change will affect community structure is unknown. We incubated a mixed natural diatom community from coastal New Zealand waters in a short-term (two-week) incubation experiment using a factorial matrix of warming and/or elevated pCO2 and measured effects on community structure. We then isolated the dominant diatoms in clonal cultures and conditioned them for 1 year under the same temperature and pCO2 conditions from which they were isolated, in order to allow for extended selection or acclimation by these abiotic environmental change factors in the absence of interspecific interactions. These conditioned isolates were then recombined into 'artificial' communities modelled after the original natural assemblage and allowed to compete under conditions identical to those in the short-term natural community experiment. In general, the resulting structure of both the unconditioned natural community and conditioned 'artificial' community experiments was similar, despite differences such as the loss of two species in the latter. pCO2 and temperature had both individual and interactive effects on community structure, but temperature was more influential, as warming significantly reduced species richness. In this case, our short-term manipulative experiment with a mixed natural assemblage spanning weeks served as a reasonable proxy to predict the effects of global change forcing on diatom community structure after the component species were conditioned in isolation over an extended timescale. Future studies will be required to assess whether or not this is also the case for other types of algal communities from other marine regimes.

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It is important to be able to predict changes in the location of populations and industries in regions that are in the process of economic integration. The IDE Geographical Simulation Model (IDE-GSM) has been developed with two major objectives: (1) to determine the dynamics of locations of populations and industries in East Asia in the long-term, and (2) to analyze the impact of specific infrastructure projects on the regional economy at sub-national levels. The basic structure of the IDE-GSM is introduced in this article and accompanied with results of test analyses on the effects of the East West Economic Corridor on regions in Continental South East Asia. Results indicate that border costs appear to play a big role in the location choice of populations and industries, often a more important role than physical infrastructures themselves.

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Usability is the capability of the software product to be understood, learned, used and attractive to the user, when used under specified conditions. Many studies demonstrate the benefits of usability, yet to this day software products continue to exhibit consistently low levels of this quality attribute. Furthermore, poor usability in software systems contributes largely to software failing in actual use. One of the main disciplines involved in usability is that of Human-Computer Interaction (HCI). Over the past two decades the HCI community has proposed specific features that should be present in applications to improve their usability, yet incorporating them into software continues to be far from trivial for software developers. These difficulties are due to multiple factors, including the high level of abstraction at which these HCI recommendations are made and how far removed they are from actual software implementation. In order to bridge this gap, the Software Engineering community has long proposed software design solutions to help developers include usability features into software, however, the problem remains an open research question. This doctoral thesis addresses the problem of helping software developers include specific usability features into their applications by providing them with a structured and tangible guidance in the form of a process, which we have termed the Usability-Oriented Software Development Process. This process is supported by a set of Software Usability Guidelines that help developers to incorporate a set of eleven usability features with high impact on software design. After developing the Usability-oriented Software Development Process and the Software Usability Guidelines, they have been validated across multiple academic projects and proven to help software developers to include such usability features into their software applications. In doing so, their use significantly reduced development time and improved the quality of the resulting designs of these projects. Furthermore, in this work we propose a software tool to automate the application of the proposed process. In sum, this work contributes to the integration of the Software Engineering and HCI disciplines providing a framework that helps software developers to create usable applications in an efficient way.

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Software Product Line Engineering (SPLE) is becoming widely used due to the improvement it means when developing software products of the same family. However, SPLE demands long-term investment on a product-line platform that might not be profitable due to rapid changing business settings. Since Agile Software Development (ASD) approaches are being successfully applied in volatile markets, several companies have suggested the idea of integrating SPLE and ASD when a family product has to be developed. Agile Product Line Engineering (APLE) advocates the integration of SPLE and ASD to address their lacks when they are individually applied to software development. A previous literature re-view of experiences and practices on APLE revealed important challenges about how to fully put APLE into practice. Our contribution address several of these challenges by tailoring the agile method Scrum by means of three concepts that we have defined: plastic partial components, working PL-architectures, and reactive reuse.

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Nanofabrication has allowed the development of new concepts such as magnetic logic and race-track memory, both of which are based on the displacement of magnetic domain walls on magnetic nanostripes. One of the issues that has to be solved before devices can meet the market demands is the stochastic behaviour of the domain wall movement in magnetic nanostripes. Here we show that the stochastic nature of the domain wall motion in permalloy nanostripes can be suppressed at very low fields (0.6-2.7 Oe). We also find different field regimes for this stochastic motion that match well with the domain wall propagation modes. The highest pinning probability is found around the precessional mode and, interestingly, it does not depend on the external field in this regime. These results constitute an experimental evidence of the intrinsic nature of the stochastic pinning of domain walls in soft magnetic nanostripes

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Accumulating evidence suggests a role for the medial temporal lobe (MTL) in working memory (WM). However, little is known concerning its functional interactions with other cortical regions in the distributed neural network subserving WM. To reveal these, we availed of subjects with MTL damage and characterized changes in effective connectivity while subjects engaged in WM task. Specifically, we compared dynamic causal models, extracted from magnetoencephalographic recordings during verbal WM encoding, in temporal lobe epilepsy patients (with left hippocampal sclerosis) and controls. Bayesian model comparison indicated that the best model (across subjects) evidenced bilateral, forward, and backward connections, coupling inferior temporal cortex (ITC), inferior frontal cortex (IFC), and MTL. MTL damage weakened backward connections from left MTL to left ITC, a decrease accompanied by strengthening of (bidirectional) connections between IFC and MTL in the contralesional hemisphere. These findings provide novel evidence concerning functional interactions between nodes of this fundamental cognitive network and sheds light on how these interactions are modified as a result of focal damage to MTL. The findings highlight that a reduced (top-down) influence of the MTL on ipsilateral language regions is accompanied by enhanced reciprocal coupling in the undamaged hemisphere providing a first demonstration of “connectional diaschisis.”