Understanding the first order controls over resource cycling and limitation in ecosystems is critical for predicting ecosystem response to disturbances. Topography and vegetation self-organizing mechanisms are first order controls over resource fluxes across the landscape. Topography controls downslope flow of resources (i.e water and nutrients). Through spatial feedbacks, vegetation is able to actively modify its environment and maximize resource flows towards it. To date, the impacts of these controls on ecosystem dynamics have mostly been investigated separately. As such, there is a knowledge gap in the understanding of how these first order controls together dictate the dynamics of the ecosystem. This dissertation aims to gain a better understanding of how self-organizing mechanisms and topography operate together to affect wetland ecosystem dynamics. A spatially explicit, wetland vegetation patterning model that includes for both vegetation self-organizing control and topographic control is developed (Nutrient Depletion Model, NDM). The model describes a scale dependent feedback between vegetation, transpiration and nutrient accumulation that drives the formation of vegetation patterns. The model is applied to investigate the effects of topography and self-organizing mechanisms on form and orientation of vegetation patterns and vegetation growth dynamics of wetland ecosystems. Results show that the two first order controls synergistically impact the formation of the various patterns as observed in wetland ecosystems. Results also show the following: (1) Self-organizing mechanisms result in a more efficient retention of resources, which result in higher biomass in the model that include for both self-organizing mechanism and topographic control (SO+TC) than in the model that that includes only for topographic control (TC). (2) However, when resources or topographic gradients increase or annual rainfall decrease, the vegetation growth dynamics of the TC+SO and TC models converge. The NDM is applied to arctic Alaska to investigate how do the two first order controls impact present and future C-N dynamics of an arctic ecosystem. Simulation results show no significant difference in the dynamics between the SO+TC model and the TC model. The climate change simulation results suggest that changes in daily variability of temperature and precipitation can impact ecosystem dynamics as much as the changes in mean temperature and precipitation. Results from this dissertation provide a more complete picture on the relative roles of the two first order controls over ecosystem nutrient cycling and vegetative growth dynamics. Finally, in this thesis, in order to simulate small-scale feedbacks over large spatial domains, the NDM is implemented in a GPU computing language, which accelerates computational simulation by at least two orders of magnitude. These tools for grid-based simulations can provide a platform for using GPUs in other areas of scientific investigation.

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Esta tesis se dedica en un estudio de estabilidad no lineal de la morfodinàmica de la zona de rompientes de playas de arena. El modelo numérico MORFO55 resuelve las ecuaciones de aguas someras no lineales para la hidrodinámica y actualiza la topografía a partir del transporte de sedimento. En primer lugar, se aplica en el caso de playas complejas longitudinalmente no uniformes con objeto de probar sus distintas formulaciones. En secundo lugar, se usa para estudiar la generación de estructuras rítmicas en playas longitudinalmente uniformes. Entre estos patrones se distinguen las barras transversales y oblicuas, las barras crescenticas y los sistemas de barras/surcos (ridges/runnels). La hipótesis de que emergen a partir de inestabilidades internas del acoplamiento entre la topografía y la hidrodinámica se investiga. Los estudios previos de modelización numérica se limitaban a las etapas iniciales de la generación de las barras. En particular, mostraban que las barras transversales y oblicuas pueden formarse en playas planas mientras que las barras crecenticas aparecen en playas con barra. La formación de los sistemas de barras/surcos se explica con modelos conceptuales de la observación mediante satélite según los cuales emergerán a partir de la deformación de la barra intermareal. Esta tesis estudia el régimen no lineal de la evolución de todos estos sistemas. Particularmente se obtiene un estado 'nal de equilibrio. Los resultados generales coinciden cualitativamente con las barras observadas en la naturaleza. Se da una interpretación física de la formación, de la evolución y de la saturación del crecimiento de las barras. / This thesis performs a nonlinear stability study of the surf zone morphodynamics of sandy beaches. To this end the MORFO55 model based on a wave and depth averaged nonlinear shallow water equations solver with wave driver, sediment transport and bed updating is presented. It is first applied to complex longitudinally non-uniform beaches in order to test different model formulations. Second, it is applied to study the generation of surf zone rhythmic features on alongshore uniform beaches. Shore-attached transverse or oblique bars, crescentic bars and ridge and runnel systems are well known examples of such features. The hypothesis that they emerge by self organisation of the coupling between topography, waves and currents is here tested. In absence of shore-parallel bars, the initial formation of transverse and oblique bars had been shown by previous modelling studies of linear stability analysis but is now extended to the finite amplitude regime. In most of barred beaches, crescentic bars and ridge and runnel systems appear. Conceptual models based on field observations suggest that ridges and runnels could emerge by the deformation of the alongshore intertidal bar intercepted by crescentic bars. Up to now, only the formation of crescentic bars had numerically succeeded with linear and non linear models. This study shows that a dynamical equilibrium state of each of these rhythmic bar systems may be described with a numerical model. General results are in qualitative agreement with the bar systems observed in nature. A physical explanation for their formation, their evolution and the saturation of their growth is given.

With the trend of using of Internet and multimedia, e-Learning has became an important learning method. e-Learning is easy to use and bring into practice, but it also has the defects inversely. One of those defects is the reuse of important and valuable discussing knowledge from asynchronous discussion boards. Nobody has time and be willing to make effort to manage the important discussion from asynchronous discussion boards in e-Learning except enthusiastic teachers or assistants. All of us know that asynchronous discussion boards is an important tool used in e-Learning for communicating and discussing with all class information for teachers and students. And reusing of important class discussing knowledge can aid teachers and students to teach and study with efficiency and effect. But up to the present, there are few researches in this domain. So, in this research we create an automatic essential content extraction method from asynchronous discussion boards in e-Learning. We explain the usage, management, and shortcomings of asynchronous discussion boards in e-Learning before. And we also describe the designing process of the research in detail. Finally, we describe the operation and the result of content extraction in this research system. All of those are hope to help teachers and students can reuse the valuable knowledge easily and quickly from past class discussion in e-Learning.

OOPS stands for Opensource Opencourseware Prototype System, a project sponsored by Fantasy Foundation. Aiming to benefit Chinese readers, this project recruit volunteer translators all over the world through internet to translate Opencourseware materials from Massachusetts Institute of Technology (MIT) into Chinese. This research was a qualitative case study conducted between 2004/2 ~ 2007/1. Multiple data sources were surveyed, including OOPS¡¦ online discussion forum, and archival information from OOPS website. Online archival data ranged from media reports, activity reports, e-newsletters, volunteer reports, survey summaries, and sub-group websites. Interviews with group leaders were also conducted. Evidence collected through these means were used to describe how OOPS employed the Internet to coordinate translation efforts and promote Opencourseware. In addition, this research applied Science of Complexity to explain the self organizing phenomenon within the network arisen from its participants. This research looked further into how Science of Complexity can clarify the organic process of a self organizing network going from simple to complex. This research found 1) the degree of openness in a collaborative knowledge network influenced its degree of self organization; 2) volunteer¡¦s willingness to participate was related to environment¡¦s fitness; 3) critical mass, diversity, variety, interaction and feedback promoted evolution; 4) a collaborative knowledge network¡¦s key to an organic expansion depended on participants¡¦ outgrowth and self organization; and 5) effective facilitation at the edge of chaos would foster new organization growth.

Nowadays, volatile and complex environment has forced most organizations to operate in team-based ways to increase their flexibility and adaptability. For teams to adapt, local innovation and change, that is, self-organization, is the most critical process. However, the self-organizing process is poorly understood both in academic and practice. To deep our understanding of self-organizing teams, this research attempts to explore the self-organizing mechanism in group cognitive system perspective. One System Dynamics model is built to represent important self-organization processes. And the classical self-organizing theory-Dissipative Structure Theory is applied to guide important simulations to acquire knowledge of dynamic interactions among those processes. Several positive loops are found to be quite essential in structuring and de-structuring team¡¦s operation structure. With the knowledge of evolutionary feedback acquired, impact of critical environmental factors, such as knowledge redundancy, communication quality, and open interactions, are further investigated and experimented.

<p>This thesis aims to evaluate four artificial neural network architectures, each of which implements the sensory-motor mapping in an embodied, situated, and autonomous agent set up to reach a goal area in one out of six systematically varied T-maze environments. In order to reach the goal the agent has to turn either to the left or to the right in each junction in the environment, depending on the placement of previously encountered light sources. The evaluation is broken down into (i) measuring the reliability of the agents' capacity to repeatedly reach the goal area, (ii) analyzing how the agents work, and (iii) comparing the results to related work on the problem.</p><p>Each T-maze constitutes an instance of a broad class of problems known as delayed response tasks, which are characterized by a significant (and typically varying) delay between a stimulus and the corresponding appropriate response. This thesis expands this notion to include, besides simple tasks, repeated and multiple delayed response tasks. In repeated tasks, the agent faces several stimulus-delay-response sequences after each other. In multiple tasks, the agent faces several stimuli before the delay and the corresponding appropriate responses. Even if simple at an abstract level, these tasks raise some of the fundamental issues within cognitive science and artificial intelligence such as whether or not an internal objective world model is necessary and/or suitable to achieve the appropriate behavior. For such reasons, these problems also constitute an interesting base for evaluating alternative ideas within these fields.</p><p>The work leads to several interesting insights. Firstly, purely reactive controllers (as represented by a feed-forward network) may be sufficient, in interaction with the environment, to solve both simple and repeated delayed response tasks. Secondly, an extended sequential cascaded network that selectively replaces its own sensory-motor mapping achieves significantly better performance than the other networks. This indicates that selective replacement of the sensory-motor mapping may be more powerful than both modulation (as represented by a simple recurrent network) and replacement in each step (as represented by a standard sequential cascaded network). Thirdly, this thesis demonstrates that even reactive controllers may contribute to behavior, which, from an observer's point of view, may seem to require an internal rational capacity, i.e. the ability to represent and explore alternatives internally.</p>

Cilien und eukariotische Flagellen sind lange, dünne Fortsaetze von Zellen. Sie enthalten eine Struktur namens Axonem. Die wesentlichen Komponenten des Axonems sind die Filamente und Motorproteine namens Mikrotubuli und Dynein. Die Motoren forcieren die Filamente, sich in oszillierender Weise gegeneinander zu verschieben, was zu einem Schlagmuster entlang des Axonemes fuehrt. Wie diese Motoren koordiniert werden und wie dieses Phaenomen quantitativ beschrieben werden kann, ist nicht verstanden. Wir studierten die Wellenformen an Spermienschwaenzen, welche ein solches Axonem enthalten, unter verschiedenen Bedingungen mit einer Hochgeschwindigkeitskamera. Wir entwickelten eine automatisierte Bildanalyse-Software, die es erlaubt, lange Zeitreihen solcher Wellenformen von Filmen zu extrahieren. In einer anschließenden Fourieranalyse erzielten wir eine gemittelte Wellenform mit erhoehter Präzision. Ein Vergleich von unseren Daten mit den Vorhersagen einer Theorie (Camalet, Julicher et al. 1999) führte zu einer Diskrepanz. Entsprechend schlugen wir eine Erweiterung der Theorie vor, indem wir annahmen, daß an der Basis des Axonems ein viskos-elastisches Element existiert. Dies führte zu einer zufrieden stellenden Übereinstimmung zwischen Theorie und Experiment. Abschließend diskutieren wir offene Fragen und zukünftige Experimente. Als ein Nebenprodukt entdeckten wir ein neues Phaenomen, bei welchem Spermien Anordnungen von dynamischen Strudeln (Vortices) bilden. Wir beschrieben dieses Phaenomen im Detail und führten einen neuen Ordnungsparameter ein, mit dem die Ordnung zwischen vielen Objekten quantifiziert werden kann. Mittels dieses Ordnungsparameters konnten wir zeigen, daß dieses Muster sich erst ab einer kritischen Dichte herausbildet. Wir schlugen ein Model vor, um den Ursprung des Musters zu erklären. Die Simulation des Models zeigte volle Uebereinstimmung mit den wesentlichen Eigenschaften dieses Musters. Weiterhin schaetzten wir die typische Wechselwirkungskraft zwischen aktiven Axonemen mit 0.1 pN ab. Abschließend ziehen wir Schlußfolgerungen über die kollektive Wirkung von Axonemen im Allgemeinen mit Hinblick auf Spermienkooperation und metachronale Cilienwellen. - Die Druckexemplare enthalten jeweils eine CD-ROM als Anlagenteil: QuickTimeMovies (ca. 65 MB) Nutzung: PLAY32 - Übersicht über Inhalte siehe Dissertation S. 108 - 109 / Cilia and eukaryotic flagella are long, thin extensions of cells that contain a structure known as axoneme. The key components of the axoneme are microtubule filaments and the motor proteins dynein. These dynein motors force the microtubules to slide in an oscillatory fashion leading to a wave pattern along the axoneme. How these motors are coordinated and how this phenomenon can be described quantitatively is not understood. I therefore studied the waveforms of sperm tails that contain such an axoneme. I observed these waveforms under different conditions with a high-speed camera and developed an automated image analysis tool allowing the extraction of long time series of this waveform. In a subsequent Fourier analysis I increased the precision by obtaining an averaged waveform. I then compared the data to the predictions of a theoretical framework (Camalet, Julicher et al. 1999) and found that they do not agree. I suggested extending this theoretical framework by considering a visco-elastic element at the base of the axoneme, which leads to a satisfactory agreement. This project leaves open questions hence further work is discussed. As a side finding, I discovered a new phenomenon on how spermatozoa form dynamic vortex arrays. I described this pattern in detail and introduced a novel order parameter to quantify the order among many particles. I showed that the array only forms above a critical sperm density. I suggested a model to explain the origin of the pattern and showed by simulation that the model can account for the main features of the pattern. Finally I estimated the typical interaction force between beating axonemes to be 0.1 pN and drew conclusions about their collective action in general that might be relevant for sperm cooperation or metachronal waves of cilia.

Trotz genauer Produktionsplanung und -steuerung mit modernen Algorithmen beobachtet man in Fabriksystemen immer wieder plötzliche und unvorhergesehene Zusammenbrüche der Materialströme. Erstaunlicherweise scheinen diese Kapazitätseinbrüche nur wenig durch die aktuelle Pufferauslastung beeinflusst zu sein. Um die entsprechenden Effekte zu unterbinden, wird in diesem Aufsatz eine neuartige Strategie zur Selbstorganisation individueller Güter in Transportund Puffersystemen vorgestellt. Durch ein kooperatives („soziales“) Verhalten dieser Güter lassen sich deren gegenseitige Behinderungen reduzieren, was zu einer deutlichen Harmonisierung des Materialflusses in der innerbetrieblichen Logistik führt. Das vorgeschlagene Konzept wird an einer beispielhaften Fabrik illustriert. Im Rahmen eines erfolgreichen Modellprojekts wird seine praktische Umsetzung derzeit bei einem englischen Verpackungshersteller erprobt. / Despite careful production planning and control using modern algorithms, one can repeatedly observe sudden and unpredicted breakdowns of the material flows in factory systems. Surprisingly, these capacity dips are only marginally affected by the current buffer storage level. To enable prevention of these effects, this paper describes a new strategy for the self-organisation of individual goods in material handling systems. Where the behaviour of the individual goods is cooperative (“social”), their mutual hindrances can be reduced, which in turn leads to a noticeable smoothing of the intra-plant material flows. The suggested concept will be illustrated with a factory example. Its practical applicability is currently being tested within the scope of a successful pilot project with a packaging manufacturer.

This diploma thesis presents experimental evidence of a theoretical concept which predicts the self-organization of delta-layers of silicon nanoclusters in the buried oxide of a MOS-like structure. This approach of "bottom-up" structuring might be of eminent importance in view of future semiconductor memory devices. Unconventionally, a 15nm thin SiO2 layer, which is enclosed by a 50nm poly-Si capping layer and the Si substrate, is irradiated with Si+ ions. Ion impact drives the system to a state far from thermodynamic equilibrium, i.e. the local composition of the target is modified to a degree unattainable in common processes. A region of SiOx (x<2) - where x is a function of depth - is formed which is not stable. During annealing, the system relaxes towards equilibrium, i.e. phase separation (via spinodal decomposition and nucleation) sets in. Within a certain time window of annealing, the structure of the system matches with a structure similar to the multidot non-volatile memory device, the principal character of which is a 2D layer of Si nanoclusters of ~3nm in diameter which is embedded in a 3D SiO2 matrix at a distance of ~3nm from the Si substrate. The physical mechanisms of ion mixing of the two Si-SiOx interfaces and subsequent phase separation, which result in the desired sample structure, are elucidated from the viewpoint of computer simulation. In addition, experimental evidence is presented based on various methods, including TEM, RBS, and SIMS. Of particular importance is a novel method of Si nanocluster decoration which applies Ge as contrast enhancing element in TEM studies of tiny Si nanoclusters.