Mechanics of fiber-reinforced hyperelastic solids

Recent designs for deployable space structures include elements that can be folded to high curvatures and recover elastically. A type of material proposed for such hinges is fiber composites with a soft silicone matrix. This research focuses on the characterization of this type of composites. Their mechanical properties during folding have been studied experimentally, revealing a highly non-linear moment-curvature relationship and stress softening, due to microdamage. The micromechanics of the problem have also been studied numerically, with a finite element model that takes into account the arrangement of the fibers. The model predicts most of the features observed experimentally, including the microbuckling that reduces fiber strain during folding. The model overestimates the material stiffness, due to its inability to model the damage taking place in the material. Current efforts are focused on modeling this damage process. In order to do so, the tension stiffness transverse to the fibers has been measured. Preliminary results including cohesive elements that delamination show good agreement with the tests

Small Businesses Encounters with Information Technology

This dissertation advances the concept of IT encountering, defined as the process whereby individuals pay attention, interpret and respond to cues suggesting changes to IT, in ways that appear sensible to them, and it studies IT encountering in the context of small businesses. I review the literatures on organizational IT adoption and IT selection, and conclude that these literatures have relied on assumptions which leave unattended important aspects of the process leading to choice: the adoption literature presupposes the saliency and significance of a focal technology to a decision maker, and the IT selection literature generally assumes that suitable IT alternatives are known to the individual making choices. The reliance on these assumptions has resulted in blind spots, which have in turn led to deficiencies in our conceptualizations. I discuss these blind spots, some historical and methodological reasons behind them, and their theoretical implications (i.e., the perpetuation of the pro-innovation bias, the absence of search from our theories, and the unexplained gaps between competing explanations of IT choice). The IT encountering perspective draws primarily on the behavioural, sensemaking, and mindfulness research traditions. Those foundations inform the empirical study, which was based on a longitudinal qualitative design, and included event-driven interviews with small business owners. The findings of the study uncover crucial aspects of the cognitive work and behavioural responses carried out by business owners during IT encounters. These aspects are composed together into a process model. My findings are consistent with previous work in noting a considerable time lag between awareness and adoption of IT innovations among small businesses, and in highlighting the crucial role of knowledge therein. The findings also differ from prior research on this topic, especially by considering a much wider range of responses and outcomes lying in between adoption and rejection of IT (e.g., tinkering, experimentation, downscaling), and by taking into account the dialectics and temporal limits of effected IT change. This alternative perspective opens up research avenues beyond the context of study, and can also guide research efforts more attuned to the views and needs of such fundamental socioeconomic actors as small businesses

Social influence and position effects

A wide range of personal choices rely on the opinions or ratings of other individuals. This information has recently become a convenient way of simplifying the decision process. For instance, in online purchases of products and services, the possible choices or alternatives are often characterized by their position in a certain presentation order (or list) and their popularity, derived from an aggregate signal of the behavior of others. We have performed a laboratory experiment to quantify and compare popularity (or social influence) and position effects in a stylized setting of homogeneous preferences, with a small number of alternatives but considerable time constraints. Our design allows for the distinction between two phases in the decision process: (1) how agents search (i.e., not only which alternatives are analyzed but also in which order) and (2) how they ultimately choose. We find that in this process there are significant popularity and position effects. Position effects are stronger than social influence effects for predicting the searching behavior, however, social influence determines to a larger extent the actual choice. The reason is that social influence generates a double effect; it directly affects the final choice (independently on what alternative has been searched more thoroughly) and indirectly alters choice through the searching behavior which, in turn, is also affected by popularity. A novelty of our approach is that we account for personal traits and provide an individual analysis of sensitivity to both social influence and position effects. Surprisingly, we find that overconfident individuals are more influenceable, whereas other personal characteristics (e.g., gender and risk aversion) do not play a significant role in this context

Training a Convolutional Neural Network for Appearance-Invariant Place Recognition

Place recognition is one of the most challenging problems in computer vision, and has become a key part in mobile robotics and autonomous driving applications for performing loop closure in visual SLAM systems. Moreover, the difficulty of recognizing a revisited location increases with appearance changes caused, for instance, by weather or illumination variations, which hinders the long-term application of such algorithms in real environments. In this paper we present a convolutional neural network (CNN), trained for the first time with the purpose of recognizing revisited locations under severe appearance changes, which maps images to a low dimensional space where Euclidean distances represent place dissimilarity. In order for the network to learn the desired invariances, we train it with triplets of images selected from datasets which present a challenging variability in visual appearance. The triplets are selected in such way that two samples are from the same location and the third one is taken from a different place. We validate our system through extensive experimentation, where we demonstrate better performance than state-of-art algorithms in a number of popular datasets

Role of Cerebellar Interpositus Nucleus in the Genesis and Control of Reflex and Conditioned Eyelid Responses

The role of cerebellar circuits in the acquisition of new motor abilities is still a matter of intensive debate. To establish the contribution of posterior interpositus nucleus (PIN) to the performance and/or acquisition of reflex and classically conditioned responses (CRs) of the eyelid, the effects of microstimulation and/or pharmacological inhibition by muscimol of the nucleus were investigated in conscious cats. Microstimulation of the PIN in naive animals evoked ramp-like eyelid responses with a wavy appearance, without producing any noticeable plastic functional change in the cerebellar and brainstem circuits involved. Muscimol microinjections decreased the amplitude of reflex eyeblinks evoked by air puffs, both when presented alone or when paired with a tone as conditioned stimulus (CS). In half-conditioned animals, muscimol injections also decreased the amplitude and damped the typical wavy profile of CRs, whereas microstimulation of the same sites increased both parameters. However, neither muscimol injections nor microstimulation modified the expected percentage of CRs, suggesting a major role of the PIN in the performance of eyelid responses rather than in the learning process. Moreover, the simultaneous presentation of CS and microstimulation in well trained animals evoked CRs similar in amplitude to the added value of those evoked by the two stimuli presented separately. In contrast, muscimol-injected animals developed CRs to paired CS and microstimulation presentations, larger than those evoked by the two stimuli when presented alone. It is concluded that the PIN contributes to the enhancement of both reflex and conditioned eyelid responses and to the damping of resonant properties of neuromuscular elements controlling eyelid kinematics

Epileptic Encephalopathies in Infants and Children

Epileptic encephalopathies represent a group of devastating epileptic disorders that appear early in life. They are characterized by pharmacoresistant generalized or focal seizures, persistent severe EEG abnormalities, and cognitive dysfunction or decline. The ictal and interictal epileptic discharges are age-specific and either are the main cause or contribute to cognitive deterioration in the idiopathic or symptomatic group, respectively. Despite choosing the most appropriate antiepileptic drugs for the seizure type and syndrome, the results are often disappointing, and polytherapy and/or alternative therapy becomes unavoidable; in those cases, consideration should be given to the quality of life of the child and carers. In this chapter, we will discuss the clinical and electroencephalographic characteristics and evolution and management of age-related epileptic encephalopathies, recognized by the International League Against Epilepsy, as follows: early infantile epileptic encephalopathy (Ohtahara syndrome), early myoclonic encephalopathy, epilepsy of infancy with migrating focal seizures, infantile spasms (West syndrome), severe myoclonic epilepsy in infancy (Dravet syndrome), myoclonic-atonic epilepsy (Doose syndrome), Lennox-Gastaut syndrome, epileptic encephalopathy with continuous spike-and-wave during sleep, and Landau-Kleffner syndrome. Their clinical features, prognosis, etiologies, and treatment are presented and updated

Biocatalytic modification of food lipids: reactions and applications

The acylglycerol structure exemplifies the major lipid building block and therefore is an interesting structure to modify. Such modification is driven by: (1) consumers who have become more concerned about the relationship between diet and wellness, and (2) new and novel functional compounds can be prepared when the original structure of a lipid is modified. This trend has led to the design of functional foods or nutraceuticals, namely, fortified, enriched, modified and enhanced foods. Advances in the biochemistry and engineering of enzymatic reactions and reactors have improved the knowledge and understanding of such reaction systems and thus, make available a generation of structured lipids. In the present work, we detail several eorts carried out to prepare novel compounds, as well as industrial applications and possible future enzymatic procedures to obtain new food products

Metodología de cálculo de NOx en generadores de vapor que queman gas natural

Este trabajo presenta la metodología para el cálculo de emisiones de NOx en un generador de vapor de 350 ton/h quemando gas natural y se investigan los métodos de control de NOx durante la combustión. Hoy en día es uno de los principales problemas de las plantas termoeléctricas puesto que genera un alto nivel de emisiones de óxidos de nitrógeno a la atmósfera. Esta metodología consiste en la determinación de los cuatro parámetros fundamentales que intervienen en la formación de NOx y son los siguientes: coeficiente de exceso de aire en la zona de combustión activa (ZCA) ¿ZCA, la temperatura promedio de la ZCA TZCA, el flujo de calor reflejado en ZCA qrefl ZCA y el tiempo de residencia de los gases en ZCA ¿ZCA. Para poder determinar estos parámetros se tiene que considerar la composición del gas natural, la transferencia de calor en el horno, las condiciones de funcionamiento y las dimensiones del generador de vapor, entre otros factores. Los cuatro parámetros principales se sustituyen en el polinomio experimental para el combustible en cuestión y, de esta forma, se puede determinar la emisión de NOx para los métodos de combustión que se analizarán en el presente artículo: recirculación de gases, diferentes lugares de introducción de gases de recirculación, combustión a dos etapas e inyección de agua