Les modèles de pile de sable sont une sous-classe d'automates cellulaires. Bak et al. les ont introduit en 1987 comme une illustration de la notion intuitive d'auto-organisation critique.Le modèle de pile de sable Kadanoff est un système dynamique discret non-linéaire imagé par des grains cubiques se déplaçant de colonne parfaitement empilée en colonne parfaitement empilée. Pour un paramètre p fixé, une règle d'éboulement est appliquée jusqu'à atteindre une configuration stable, appelée point fixe : si la différence de hauteur entre deux colonnes consécutives est strictement supérieure à p, alors p grains chutent de la colonne de gauche, un retombant sur chacune des p colonnes adjacentes sur la droite.A partir d'une règle locale simple, décrire et comprendre le comportement macroscopique des piles de sable s'avère très rapidement compliqué. La difficulté consiste en la prise en compte simultanée des modalités discrète et continue du système : vue de loin, une pile de sable s'écoule comme un liquide ; mais de près, lorsque l'on s'attache à décrire exactement une configuration, les effets de la dynamique discrète doivent être pris en compte. Si par exemple nous ajoutons un unique grain à une configuration stable, celui-ci déclenche une avalanche qui ne modifie que la couche supérieure de la pile, mais dont la taille est très difficile à prédire car sensible au moindre changement sur la configuration.En analogie avec un sablier, nous nous intéressons en particulier à la séquence des points fixes atteints par l'ajout répété d'un nombre fini de grains à une même position, et à l'émergence de structures étonnamment régulières.Après avoir établi une conjecture sur l'émergence de motifs de vague sur les points fixes, nous nous pencherons dans un premier temps sur une procédure inductive de calcul des points fixes. Chaque étape de l'induction correspond au calcul d'une avalanche provoquée par l'ajout d'un nouveau grain, et nous en proposerons une description simple. Cette étude sera prolongée par la définition de trace des avalanches sur une colonne i, qui capture dans un mot d'un alphabet fini l'information nécessaire à la reconstitution du point fixe pour les colonnes à la droite de l'indice i. Des liens entre les traces à des indices successifs seront alors exploités, liens qui permettent de conclure l'émergence de traces régulières, pour lesquelles la reconstitution du point fixe implique la formation des motifs de vague observés. Cette première approche est concluante pour le plus petit paramètre conjecturé jusqu'ici, p=2.L'étude du cas général que nous proposons passe par la construction d'un nouveau système mêlant différentes représentations des points fixes, qui sera analysé par l'association d'arguments d'algèbre linéaire et combinatoires (liés respectivement aux modalités continue et discrète des piles de sable). Ce résultat d'émergence de régularités dans un système dynamique discret fait appel à des techniques nouvelles, dont la compréhension d'un élément de preuve reste en particulier à raffiner, ce qui permet d'envisager un cadre plus général d'appréhension de la notion d'émergence. / Sandpile models are a subclass of Cellular Automata. Bak et al. introduced them in 1987 for they exemplify the intuitive notion of Self-Organized Criticality.The Kadanoff sandpile model is a non-linear discrete dynamical system illustrating the evolution of cubic sand grains from nicely packed columns to nicely packed columns. For a fixed parameter p, a rule is applied until reaching a stable configuration, called a fixed point : if the height difference between two consecutive columns is strictly greater than p, then p grains fall from the left column, one landing on each of the p adjacent columns on the right.From a simple local rule, to describe and understand the macroscopic behavior of sandpiles is very quickly challenging. The difficulty consists in the simultaneous study of continuous and discrete aspects of the system: on a large scale, a sandpile flows like a liquid; but on a small scale, when we want to describe exactly the shape of a fixed point, the effects of the discrete dynamic must be taken into account. If for example we add a single grain on a stabilized sandpile, it triggers an avalanche that roughly changes only the upper layer of the configuration, but which size is hard to predict because it is sensitive to the tiniest change of the configuration.In analogy with an hourglass, we are particularly interested in the sequence of fixed points reached after adding a finite number of grains on one position, with the aim of explaining the emergence of surprisingly regular patterns.After conjecturing the emergence of wave patterns on fixed points, we firstly consider an inductive procedure for computing fixed points. Each step of the induction corresponds to the computation of an avalanche triggered by the addition of a new grain, for which we propose a simple description. This study is carried on with the definition of the trace of avalanches on a column i, which catches in a word among a finite alphabet enough information in order to reconstruct the fixed point on the right of index i. Links between traces on successive columns are then investigated, links allowing to conclude the emergence of regular traces, whose fixed point's reconstruction involves the appearance and maintain of the wave patterns observed. This first approach is conclusive for the smallest conjectured parameter so far, p=2.The study of the general case goes through the design of a new system meddling in different representations of fixed points, which will be analyzed via an association of arguments of linear algebra and combinatorics (respectively corresponding to the continuous and discrete modalities of sandpiles). This result stating the emergence of regularities in a discrete dynamical system put new technics into light, for which the comprehension of a particular point in the proof remains to be increased. This motivates the consideration of a more general frame of work tackling the notion of emergence.

No description available.

Researchers have long argued the importance of shared book reading and its potential impact on future reading growth. With the increasing popularity of e-books and the introduction of interactive iPad books, more and more parents are sharing books with their children in digital format. This may have a direct impact on the nature of the interactions that occur during young children's early book sharing experiences. This multiple-case study examined the nature of the interactions between six mother-child dyads as they read a story on an iPad compared with the interactions that happened during a traditional book reading. A coding system was developed to categorize behaviors during the reading sessions. The categories included (a) meaning talk, (b) text and print talk, (c) technology talk, and (d) the nature of the affective climate.The results of this study indicate that mother-child traditional read-alouds and digital iPad read-alouds are different experiences. During digital readings there was an increase in the number of vocabulary-related (a subcategory of meaning) interactions but a decrease in the number of interactions related to text and print. The results also showed that as the dyad shared a digital storybook, they engaged in many interactions about the technological elements of the iPad texts, which may be important to the development of digital literacies in young children. The findings also indicate that a child is more engaged with digital texts than with traditional texts, which is important because engagement is an essential component in literacy development. However, sometimes the child's increased engagement with the digital texts resulted in both members of the dyad being less sensitive to the other. Digital storybook reading is a relatively new experience for many parents and thus, they may not know how to interact with their children in ways that promote the development of traditional and digital literacies.

Many American preschool children enter kindergarten without the emergent literacy skills needed to learn to read. To address this problem, this multicase qualitative study investigated the emergent literacy practices at Steiner Waldorf-inspired and Reggio Emilia-inspired schools. The research questions focused on how alternative preschool philosophies help staff cultivate emergent literacy skills in young children. The conceptual framework came from Piaget's cognitive development theory, and Vygotsky's sociocultural theory. The study included eight participants from two Reggio Emilia-inspired and two Steiner Waldorf-inspired preschools. Data were collected through open-ended interviews, observations, and analyses of de-identified student work, then subjected to thematic cross-case analysis. Regarding the role of the two philosophies in the development of emergent literacy skills, findings indicated that teachers cited the philosophies leading them to honor their students, focus on the development of the whole child, and act as facilitators for children's oral language development through play. Regarding how program staff apply their program philosophies to creating emergent literacy through the learning environment key, the findings showed that both Steiner Waldorf-inspired and Reggio Emilia-inspired staff viewed the environment as another teacher. Reggio Emilia-inspired staff carefully organized the indoor and outdoor learning environments to provide numerous opportunities for authentic experiences and play, while Waldorf-inspired staff was more likely to draw from nature itself to create opportunities for imaginary play. When children start school with a solid foundation in emergent literacy, they are more likely to be successful readers.

<p>Alternative stable states have been, based on theoretical findings, predicted to be common in ecological systems. Empirical data from a number of laboratory and natural studies strongly suggest that alternative stable states also occur in real populations, communities and ecosystems. Potential mechanisms involve population size-structure and food-dependent individual development. These features can lead to ontogenetic niche shifts, juvenile recruitment bottlenecks and emergent Allee effects; phenomena that establish destabilising positive feedbacks in a system and hence create alternative stable states.</p><p>I studied the consequences of population size-structure for community dynamics at different scales of system complexity. I performed laboratory and ecosystem experiments. Small poecilliid fishes and planktonic invertebrates with short generation times and life spans were used as model organisms. This allowed me to assess the long-term dynamics of the populations and communities investigated.</p><p>The main experimental results are: (a) An ontogenetic niche shift in individuals of the phantom midge <i>Chaoborus</i> made the population vulnerable to an indirect competitive recruitment bottleneck imposed by cladoceran mesozooplankton via rotifers. Consequentially the natural zooplankton food web exhibited two alternative attractors. (b) Body size determined the success of <i>Poecilia reticulata</i> invading resident population of <i>Heterandria formosa</i> and thus the type of alternative stable state that established. Small invaders were outcompeted by the residents, whereas large invaders excluded their competitor by predating on its recruits. (c) External juvenile and adult mortality altered the internal feedback structure that regulates a laboratory population of <i>H. formosa</i> in such a way that juvenile biomass increased with mortality. This biomass overcompensation in a prey population can establish alternative stable states with top-predators being either absent or present.</p><p>The major conclusion is that size-structure and individual growth can indeed lead to alternative stable states. The considerations of these ubiquitous features of populations offer hence new insights and deeper understanding of community dynamics. Alternative stable states can have tremendous consequences for human societies that utilise the ecological services provided by an ecological system. Understanding the effects of size-structure on alternative stability is thus crucial for sustainable exploitation or production of food resources.</p>

<p>The aim of the study was to investigate if methane emission in a constructed wetland changed in a diurnal pattern correlating to temperature, humidity or light conditions. The gas measurements were carried out with a static chamber technique. The wetland (in Nykvarn outside of Linköping, Sweden) takes care of wastewater to reduce the nitrogen loads. Measurements were carried out at three different occasions in the summer of 1998 on two sites in the wetland. One site was close to the inflow, inhabited by Lemnaceae, and another site was located further downstream inhabited by the emergent macrophyte Typha latifolia. The results showed a variation, but no discernible diurnal pattern. The Typha site had a methane emission rate of 166 mg CH₄ m-2d-1 and the Lemnaceae site had an methane emission rate of 712 mg CH₄ m-2d-1. In all experiments at the Typha site, the highest methane emission rate was obtained at sunrise.</p>

No description available.

Alternative stable states have been, based on theoretical findings, predicted to be common in ecological systems. Empirical data from a number of laboratory and natural studies strongly suggest that alternative stable states also occur in real populations, communities and ecosystems. Potential mechanisms involve population size-structure and food-dependent individual development. These features can lead to ontogenetic niche shifts, juvenile recruitment bottlenecks and emergent Allee effects; phenomena that establish destabilising positive feedbacks in a system and hence create alternative stable states. I studied the consequences of population size-structure for community dynamics at different scales of system complexity. I performed laboratory and ecosystem experiments. Small poecilliid fishes and planktonic invertebrates with short generation times and life spans were used as model organisms. This allowed me to assess the long-term dynamics of the populations and communities investigated. The main experimental results are: (a) An ontogenetic niche shift in individuals of the phantom midge Chaoborus made the population vulnerable to an indirect competitive recruitment bottleneck imposed by cladoceran mesozooplankton via rotifers. Consequentially the natural zooplankton food web exhibited two alternative attractors. (b) Body size determined the success of Poecilia reticulata invading resident population of Heterandria formosa and thus the type of alternative stable state that established. Small invaders were outcompeted by the residents, whereas large invaders excluded their competitor by predating on its recruits. (c) External juvenile and adult mortality altered the internal feedback structure that regulates a laboratory population of H. formosa in such a way that juvenile biomass increased with mortality. This biomass overcompensation in a prey population can establish alternative stable states with top-predators being either absent or present. The major conclusion is that size-structure and individual growth can indeed lead to alternative stable states. The considerations of these ubiquitous features of populations offer hence new insights and deeper understanding of community dynamics. Alternative stable states can have tremendous consequences for human societies that utilise the ecological services provided by an ecological system. Understanding the effects of size-structure on alternative stability is thus crucial for sustainable exploitation or production of food resources.

The aim of the study was to investigate if methane emission in a constructed wetland changed in a diurnal pattern correlating to temperature, humidity or light conditions. The gas measurements were carried out with a static chamber technique. The wetland (in Nykvarn outside of Linköping, Sweden) takes care of wastewater to reduce the nitrogen loads. Measurements were carried out at three different occasions in the summer of 1998 on two sites in the wetland. One site was close to the inflow, inhabited by Lemnaceae, and another site was located further downstream inhabited by the emergent macrophyte Typha latifolia. The results showed a variation, but no discernible diurnal pattern. The Typha site had a methane emission rate of 166 mg CH4 m-2d-1 and the Lemnaceae site had an methane emission rate of 712 mg CH4 m-2d-1. In all experiments at the Typha site, the highest methane emission rate was obtained at sunrise.

A comparative study between old school which is considered to be boring and out of context by (many student) to new school of teaching where divers IT and ICT gadgets are used and their implications in creating a positive teacher student relationship from the very start to promote emergent literacy within preschool class. This ethnographic study examines how two preschool class teachers incorporate both old and new methods to create interest for learning and meaningfulness among their students in accordance with the national goals for education and lifelong learning. How does IT and ICT promote teaching and learning in preschool class? In what ways do teachers incorporate into classroom experiences? What are the group dynamics between teacher- student, and student- and their peers during a classroom scenario with the conventional paper and pen and technological aid?  With these central questions the study was conducted as an participant observation which resulted in preschool class children find it lot easier to communicate not only with teachers but also with their classmates during classroom activities where IT and ICT is incorporated than when teachers take on the role what they call old school which tends to become one-sided.  The results show that creating meaningfulness among ones students is largely based upon the teachers own interest in the focus group. From a socio-cultural perspective, it is evident that terms such as interaction, meaningfulness, symbols and artifacts become central. Results from the study shows even though many in-service teachers and principals are very much for including IT and ICT as teaching resource. Ambiguity of national norms and goals when we talk of preschool classes in the nation could be one the many reasons why they fail to meet their students expectations and demands. This in turn could be one of the considerable reasons for the depression in high school students failing to meet the national educational standards. / Utgångspunkten i detta examensarbete är en jämförande studie mellan gamla skolan och dess undervisningsätt vilken anses vara tråkig och utan sammanhang bland många elever och nya skolans undervisning med IT och IKT som didaktisk undervisningsmetod. Dess konsekvenser för att skapa en positiv relation mellan lärare och elev från första början för att främja framväxande och skrivkunnighet inom förskoleklass.En etnografisk undersökning av hur två förskoleklasslärare gagnar både de gamla och nya metoderna för att skapa intresse för lärande och meningsskapande bland sina elever i enlighet med nationella målen för ett livslångt lärande och hållbar utveckling. Hur främjar IT och IKT lärandet i förskoleklassen? På vilka sätt införlivar lärare upplevelser i klassrummet. Vad är gruppdynamik mellan lärare och elev, samt gruppdynamik mellan eleverna i ett klassrumsscenario med den konventionella papper/penna och tekniska stöd? Med dessa centrala frågor genomfördes studien som en deltagande observation. Detta resulterade i att förskoleklassbarnen tycker att det är mycket lättare att kommunicera inte bara med lärare utan även med sina klasskamrater under klassrumsaktiviteter där IT och IKT ingår än när lärare tar på sig rollen i den så kallade gamla skolan som tenderar att bli ensidig. Resultaten visar att skapa meningsfullhet bland elever till stor del baseras på lärarnas eget intresse i fokusgruppen. Ur ett sociokulturellt perspektiv är det uppenbart att begrepp som interaktion, meningsfullhet, symboler och artefakter blir central. Resultaten från studien visar att det finns ett stort intresse och ambitioner från rektor och lärare att införa bland annat IT och IKT i undervisningen. På grund av tvetydigheten i de nationella målen och normer när man talar om förskoleklass har detta orsakat många lärare och skolor att misslyckas med att uppfylla elevernas förväntningar och krav, vilket i sin tur kan vara en av de stora orsakerna till det ökande antalet gymnasieelever som inte uppfyller de nationella kunskapsmålen i Sverige.