A Grounded Theory of Emergent Leadership in Nonhierarchical Virtual Teams by Randall David Fleming MS, Colorado Technical University, 2008 BA, The Ohio State University, 1984 Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Management Walden University November 2018

Les modèles structure-fonction de la croissance des plantes (FSPMs) combinent la description du fonctionnement biophysique et du développement architectural des plantes. On peut distinguer deux grandes familles de FSPM : d'une part les modèles décrivant finement la structure de la plante au niveau de l'organe et d'autre part les modèles à plus grande échelle qui s'intéressent directement à la forme du houppier. La paramétrisation du premier type de modèle est souvent difficile car elle nécessite des données expérimentales très riches. A l'inverse, les modèles à plus grande échelle mettent généralement en œuvre des lois empiriques qui ne permettent pas de décrire la plasticité de la croissance, et l'adaptation de la plante à des conditions environnementales différentes.Pour répondre à ces problématiques, nous nous tournons vers un nouveau paradigme : Motivé par le succès du concept de la densité spatiale dans les modèles en écologie des populations, cette thèse caractérise la distribution spatiale de feuillage dans les plantes par la densité de surface foliaire , ce qui permet une description locale ouvrant la voie à une prise en compte de la plasticité des plantes, tout en ne décrivant pas chaque feuille individuellement, ce qui permet de modéliser des vieux et grands arbres, dont le nombre de feuilles est sinon trop lourd à gérer du point de vue des calculs. Cette thèse présente des modèles dynamiques de croissance développés spécifiquement pour les plantes agricoles et les arbres. Nous explorons des approches mathématiques différentes en temps discrète et continue, tout en examinant d'un œil critique leurs aptitudes conceptuelles ainsi que des possibilités de simplifications et de solutions analytiques dans l'optique de l'accélération des simulations.La densité foliaire permet le calcul de l'interception de lumière par la loi de Beer-Lambert et la production de biomasse grâce au concept d'efficience d'utilisation de la lumière. Le mécanisme central qui est considéré pour les différentes approches développées dans cette thèse est celui de l'expansion locale de la surface foliaire dans la direction du gradient de lumière. Par ce concept téléonomique, nous faisons l'hypothèse que la plante cherche par son développement à optimiser la productivité de la surface foliaire pour la production de biomasse. Ce principe induit ainsi un développement horizontal et vertical du feuillage vers l'extérieur du houppier. Le développement horizontal cesse quand on s'approche trop de plantes voisines, leur ombrage diminuant le gradient de lumière et donc l'expansion de densité de surface foliaire dans ces directions. Le modèle de production de biomasse est également généralisé pour une prise en compte explicite de la teneur en eau du sol en introduisant une composante hydraulique permettant de décrire l'équilibre mécaniste entre le potentiel hydrique dans les feuilles et la transpiration par la régulation stomatale. Finalement, nous prenons en compte l'allocation de biomasse produite à d'autres compartiments de la plante tels que les racines et le bois selon la théorie du « pipe model ».Les résultats des modèles sont comparés à un large jeu de données expérimentales sur des plantations à différentes densités et conditions environnementales. Celui-ci montre de remarquables capacités d'une part à prévoir les variables biométriques importantes (hauteur, diamètre du tronc) ainsi que certaines relations d'allométrie, et d'autre part à générer des formes de houppier en accord avec les formes observées, ceci pour les différents scénarios de compétition et comme propriété émergente du modèle. Ainsi, cette thèse démontre le potentiel du concept de densité de surface foliaire en modélisation de la croissance des plantes, par sa capacité à reproduire les comportements locaux et l'adaptation à des conditions environnementales variées sans compromettre l'efficacité et la robustesse. / Functional-structural plant growth models (FSPMs) have emerged as the synthesis of mechanistic process-based models, and geometry-focussed architectural models. In terms of spatial scale, these models can essentially be divided into small-scale models featuring a topologic­al architecture – often facing data-demanding parametrisations, parameter sensitivity, as well as computational heaviness, which imposes problematic limits to the age and size of in­dividuals than can be simulated – and large-scale models based on a description of crown shape in terms of rigid structures such as empirical crown envelopes – commonly strug­gling to allow for spatial variability and plasticity in crown structure and shape in response to local biotic or abiotic growth conditions.In response to these limitations, and motivated not least by the success-story of spatial density approaches in theoretical populations ecology, the spatial distribution of foliage in plants in this thesis is characterised in terms of spatial leaf density, which allows for a com­pletely local description that is a priori unrestricted in terms of plasticity, while being robust and computationally efficient. The thesis presents dynamic growth models specific­ally developed for crops and trees, exploring different mathematical frameworks in continu­ous and discrete time, while critically discussing their conceptual suitability and exploring analyt­ical simplifications and solutions to accelerate simulations.The law of Beer-Lambert on the passing of light though an absorbing medium allows to infer the local light conditions based on which local biomass production can be computed via a radiation use efficiency. A key unifying mechanism of the different models is the local ex­pansion of leaf density in the direction of the light gradient, which coincides with the direc­tion most promising with regard to future biomass productivity. This aspect falls into the line of teleonomic and optimization-oriented plant growth models, and allows to set aside the otherwise complex modelling of branching processes. The principle induces an expans­ive horizontal and upward-directed motion of foliage. Moreover, it mechanistically accounts for a slow-down of the horizontal expansion as soon as a neighbouring competitor's crown is reached, since the appropriate region is already shaded, implying a corresponding adapta­tion of the light gradient. This automatically results in narrower crowns in scenarios of in­creased competition, ultimately decreasing biomass production and future growth due to lesser amount of intercepted light. In an extension, the impact of water availability is incor­porated into the previously light-only dependency of biomass production by means of a novel hydraulic model describing the mechanistic balancing of leaf water potential and tran­spiration in the context of stomatal control. The allocation of produced biomass to other plant compartments such as roots and above-ground wood, e.g. by means of the pipe model theory, is readily coupled to leaf density dynamics.Simulation results are compared against a variety of empirical observations, ranging from long-term forest inventory data to laser-recorded spatial data, covering multiple abi­otic environmental conditions and growth resources as well as stand densities and thus de­grees of competition. The models generate a series of complex emergent properties includ­ing the realistic prediction of biometric growth parameters, the spontaneous adaptability and plasticity of crown morphologies in different competitive scenarios, the empirically documented insensitivity of height to stand density, the accurate deceleration of height growth, as well as popular allometric relationships – altogether demonstrating the potential of leaf density based approaches for efficient and robust plant growth modelling.

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Interactions between the microscopic constituents of a solid---a many-body system--- can lead to novel phases and exotic physical phenomena like fractionalization, topological order, quantum spin liquids, emergent gauge field, etc.. The concept of frustration provides a ground for such exotic phenomena. Frustration can prevent a many-body system from establishing long-range order down to the lowest temperatures due to competing interactions. Instead, competing interactions may result in disordered and liquid-like phases of matter that provide the vacuum for fractional excitations. The absence of any order parameter in strongly frustrated systems---due to not breaking any symmetry spontaneously--- immediately raises the question about possible experimental probes of spin-liquids and their fractional excitations. Dynamic probes, like inelastic neutron scattering or Raman scattering, provide an experimental method to detect signatures of fractionalised quasiparticles. The energy and momentum transferred in a scattering event is split between the fractional quasiparticles. On the theory side, computing such dynamical signatures beyond one spatial dimension is generally a difficult task. In this thesis, numerical methods like density matrix renormalisation group and matrix product states are used to study strongly frustrated magnets and their dynamics in a non-perturbative way. This thesis covers two physical models in the context of frustration and emergent gauge fields. Firstly, the Kitaev model of spin-1/2 degrees of freedom subject to strongly anisotropic spin exchange. The Kitaev model features quantum spin liquid ground states with fractionalization of spins into Majorana fermions and Z_2-fluxes---the visons of an emergent Z_2 gauge theory. The main questions addressed here concern the stability of the quantum spin liquid phase upon adding perturbations relevant in magnetic compounds such as Heisenberg or the symmetric-offdiagonal Gamma exchange. Applying a magnetic field drives the Kitaev model into a topologically ordered phase. The excitations and dynamical signatures within the spin liquid, the topologically ordered phase, and within ordered phases are studied. Secondly, a classical minimal model of the proton configuration in water ice is studied. The ice rules, a local constraint describing the low energy manifold, result in emergent Maxwell's equation. Upon applying an external electric field along certain axis, a polarization plateau occurs in which the remaining degrees of freedom can be described by dimers on two-dimensional lattices.

In this study, we present the different teaching strategies that participating preschool teachers describe that they use to stimulate and develop children's language through fiction. We will present what factors influence the selection of fiction at the preschool. Furthermore, we describe the preschool teachers' perceptions of how they describe their conditions and knowledge of literature work together with the children. We chose to do a qualitative study where we visited different preschools to interview active preschool teachers based on semi-structured interview questions. When compiling the results, we used a phenomenographic methodological approach to obtain preschool teachers' different perceptions of the language-stimulating work. The most significant thing we were able to get in the result is that all preschool teachers in our study described an awareness of the importance of language-stimulating teaching in preschool. It also emerged that preschool teachers included language-stimulating activities through planned teaching or spontaneously arising situations. We were further able to discern in the results how the preschool teachers in our study used different strategies to stimulate children's language. Reading aloud, book conversations, image creation, dramatization and reflection conversations were some strategies that emerged. As a conclusion, through the interviews we were able to get the preschool teachers' perceptions and what conditions and challenges they experience with the language-developing work in preschool. Something that we have found important from the study is that preschool teachers' knowledge and prerequisites have a significant role in children's language development and where children's language is stimulated and challenged in social contexts. / I den här studien presenterar vi vilka olika undervisningsstrategier medverkande förskollärare beskriver att de använder sig av för att stimulera och utveckla barns språk genom skönlitteratur. Vi kommer att presentera vilka faktorer som påverkar urvalet av skönlitteratur på förskolan. Vidare redogör vi förskollärarnas uppfattningar av hur de beskriver sina förutsättningar och kunskaper kring litteraturarbete tillsammans med barnen. Vi valde att göra en kvalitativ studie där vi besökte olika förskolor för att intervjua verksamma förskollärare utifrån semistrukturerade intervjufrågor. Vid sammanställningen av resultatet utgick vi från en fenomenografisk metodansats för att få fram förskollärares olika uppfattningar om det språkstimulerande arbetet. Det mest betydelsefulla vi kunde vi få fram i resultatet var att samtliga förskollärare i vår studie beskrev en medvetenhet kring vikten av språkstimulerande undervisning i förskolan. Det framkom också att förskollärare inkluderade språkstimulerande aktiviteter genom planerad undervisning eller spontant uppkomna situationer. Vi kunde vidare i resultatet urskilja hur förskollärarna i vår studie använde sig av olika strategier för att stimulera barns språk. Högläsning, boksamtal, bildskapande, dramatisering och reflektionssamtal var några strategier som framkom. Som avslutning kunde vi genom intervjuerna få fram förskollärares uppfattningar och vilka förutsättningar och utmaningar de upplever med det språkutvecklande arbetet i förskolan. Något som vi funnit som viktigt utifrån studien är att förskollärares kunskaper och förutsättningar har en betydande roll för barns språkutveckling och där barns språk stimuleras och utmanas i sociala kontexter.

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