Dissertations / Theses on the topic 'Driven diffusive model'

In contrast to the equilibrium case, there is no general theoretical framework for the treatment of many-body nonequilibrium systems. Therefore, simple model systems, amenable to detailed analytical or numerical treatment, are important in the understanding of such systems. Phase transitions and ordering are fundamental phenomena which have been extensively studied in equilibrium statistical physics. In this work, we investigate these phenomena in several model driven diffusive systems. We introduce the 'bus route model', a simple microscopic model in which jamming of a conserved driven species is mediated by the presence of a non-conserved quantity. Jamming proceeds via a strict phase transition only in a prescribed limit; outside this limit, we find sharp crossovers and transient coarsening. Next, we study flocking, the collective motion of many self-driven entities, in a one-dimensional lattice model. We find the existence of an ordered phase characterized by the presence of a single large 'flock' which exhibits stochastic reversals in direction. Using numerical finite-size scaling, we analyse the continuous phase transition from this ordered phase to a homogeneous phase and we calculate critical exponents. Finally, we study a model of shear-induced clustering; we find evidence for a discontinuous jamming transition with hysteresis. We also study the kinetics of jamming.

In this thesis, we focus on the steady state properties of two systems which are genuinely out of equilibrium. The first project is an application of dynamic field theory to a specific non equilibrium critical phenomenon, while the second project involves both simulations and analytical calculations. The methods of field theory are used on both these projects. In the first part of this thesis, we investigate a generalization of the well-known field theory for directed percolation (DP). The DP theory is known to describe an evolving population, near extinction. We have coupled this evolving population to an environment with its own nontrivial spatio-temporal dynamics. Here, we consider the special case where the environment follows a simple relaxational (model A) dynamics. We find two marginal couplings with upper critical dimension of four, which couple the two theories in a nontrivial way. While the Wilson-Fisher fixed point remains completely unaffected, a mismatch of time scales destabilizes the usual DP fixed point. Some open questions and future work remain. In the second project, we focus on a simple particle transport model far from equilibrium, namely, the totally asymmetric simple exclusion process (TASEP). While its stationary properties are well studied, many of its dynamic features remain unexplored. Here, we focus on the power spectrum of the total particle occupancy in the system. This quantity exhibits unexpected oscillations in the low density phase. Using standard Monte Carlo simulations and analytic calculations, we probe the dependence of these oscillations on boundary effects, the system size, and the overall particle density. Our simulations are fitted to the predictions of a linearized theory for the fluctuation of the particle density. Two of the fit parameters, namely the diffusion constant and the noise strength, deviate from their naive bare values [6]. In particular, the former increases significantly with the system size. Since this behavior can only be caused by nonlinear effects, we calculate the lowest order corrections in perturbation theory. Several open questions and future work are discussed.
Ph. D.

Here, we propose a method for generating a hierarchy of mean-field approximations to study the properties of the driven diffusive Ising model at nonequilibrium steady state. In addition, the present study offers a demonstration of the practical application of the information theoretic methods to a simple interacting nonequilibrium system. The application of maximum entropy principle to the system, which is in contact with a heat reservoir, leads to a minimization principle for the generalized Helmholtz free energy. At every level of approximation the latter is expressed in terms of the corresponding mean—field variables. These play the role of variational parameters. The rate equations for the mean-field variables, which incorporate the dynamics of the system, serve as constraints to the minimization procedure. The method is applicable to high temperatures as well to the low temperature phase coexistence regime and also has the potential for dealing with first-order phase transitions. At low temperatures the free energy is nonconvex and we use a Maxwell construction to find the relevant information for the system. To test the method we carry out numerical calculations at the pair level of approximation for the 2-dimensional driven diffusive Ising model on a square lattice with attractive interactions. The results reproduce quite well all the basic properties of the system as reported from Monte Carlo simulations.
Ph. D.

Dans cette thèse, des techniques d'homogénéisation numérique efficaces en termes de calcul sont présentées pour les phénomènes de diffusion dans des matériaux hétérogènes. Comme étape préliminaire, une réduction de modèle pour l'équation de diffusion de chaleur transitoire est effectuée à la microéchelle en utilisant la synthèse en mode composants, qui fournit une description émergente enrichie-continuum à l’échelle macroscopique. Sur la base de la localisation des variables d'enrichissement, soit sur les nœuds d'éléments finis, soit sur les points de quadrature, deux schémas de discrétisation spatiale sont analysés pour le diplacement milieu continu. La formulation du potentiel chimique et des champs de déformation est utilisée, ce qui permet l'utilisation d'éléments finis continus en C0 standard. Le problème de la micro-échelle, qui implique généralement une solution coûteuse du problème de la mécanique de diffusion de masse couplée est maintenant remplacée par un ensemble d'équations différentielles ordinaires grâce à la réduction du modèle. Enfin, une approche alternative de réduction de modèle utilisant la mécanique basée sur les données est explorée. Il repose sur une recherche directe et une interpolation à partir d'une base de données au lieu de la solution d'un problème microscopique. La base de données est construite et stockée en utilisant les calculs microscopiques dans une étape hors ligne. Il fournit également une voie pour étendre la méthode de réduction du modèle proposée au régime non linéaire
In this thesis computationally efficient numerical homogenization techniques are presented for diffusion phenomena in heterogeneous materials. As a preliminary step, a model reduction for the transient heat diffusion equation is performed at the micro-scale using component mode synthesis, which provides an emergent enriched-continuum description at the macro-scale. Based on the location of the enrichmentvariables, either on the finite element nodes or the quadrature points, two spatial discretization schemes are analyzed for the enrichedcontinuum. The proposed model reduction is also extended to the transient mass diffusion coupled to the mechanics with application to lithium-ion batteries. Chemical potential and strain fields formulation is used which allows the use of standard C0-continuous finite elements. The micro-scale problem, which usually involves an expensive solution of the coupled mass diffusionmechanics problem is now replaced by a set of ordinary differential equations through model reduction. Finally, an alternative model reduction approach using data-driven mechanics is explored. It relies on a direct search and interpolation from a database instead of the solution of a microscopic problem. The database is constructed and stored using the microscopic calculations in an offline stage. It also provides a route to extend the proposed model reduction method to the nonlinear regime

In the classical theory, the fractional diffusion is ruled by two different types of fractional Laplacians. Formerly known since 60s, the spectral fractional Laplacian had an important development in the recent mathematical study with the initial contributes of L. Caffarelli, L. Silvestre and X. Cabré, X.Tan. The integral version of the fractional Laplacian, recently discussed by M. Fukushima, Y. Oshima, M Takeda, and Song, Vondracek, is considered in a semilinear elliptic problem in presence of a general logistic function and an indefinite weight. In particular we look for a multiplicity result for the associated Dirichlet problem. In the second part, starting from the classical works of T.Hillen and G. Othmer and taking the Generalized velocity jump processes presented in a recent work of J.T.King, we obtain the fractional diffusion as limit of this last processes using the technique used in another recent work of Mellet, without the classical Hilbert or Cattaneo approximation's methods.

In this thesis we study some portfolio optimization and option pricing problems in market models where the dynamics of one or more risky assets are driven by Lévy processes, and it is divided in four independent parts. In the first part we study the portfolio optimization problem, for the logarithmic terminal utility and the logarithmic consumption utility, in a multi-defaultable Lévy driven model. In the second part we introduce a novel technique to price European defaultable claims when the pre-defaultable dynamics of the underlying asset follows an exponential Lévy process. In the third part we develop a novel methodology to obtain analytical expansions for the prices of European derivatives, under stochastic and/or local volatility models driven by Lévy processes, by analytically expanding the integro-differential operator associated to the pricing problem. In the fourth part we present an extension of the latter technique which allows for obtaining analytical expansion in option pricing when dealing with path-dependent Asian-style derivatives.
In questa tesi studiamo alcuni problemi di portfolio optimization e di option pricing in modelli di mercato dove le dinamiche di uno o più titoli rischiosi sono guidate da processi di Lévy. La tesi é divisa in quattro parti indipendenti. Nella prima parte studiamo il problema di ottimizzare un portafoglio, inteso come massimizzazione di un’utilità logaritmica della ricchezza finale e di un’utilità logaritmica del consumo, in un modello guidato da processi di Lévy e in presenza di fallimenti simultanei. Nella seconda parte introduciamo una nuova tecnica per il prezzaggio di opzioni europee soggette a fallimento, i cui titoli sottostanti seguono dinamiche che prima del fallimento sono rappresentate da processi di Lévy esponenziali. Nella terza parte sviluppiamo un nuovo metodo per ottenere espansioni analitiche per i prezzi di derivati europei, sotto modelli a volatilità stocastica e locale guidati da processi di Lévy, espandendo analiticamente l’operatore integro-differenziale associato al problema di prezzaggio. Nella quarta, e ultima parte, presentiamo un estensione della tecnica precedente che consente di ottenere espansioni analitiche per i prezzi di opzioni asiatiche, ovvero particolari tipi di opzioni il cui payoff dipende da tutta la traiettoria del titolo sottostante.

Motores moleculares são proteínas capazes de transportar objetos tais como vesículas, organelas e macromoléculas ao longo do citoesqueleto. Tratam-se de dispositivos bastante interessantes do ponto de vista físico, pois produzem trabalho em um ambiente extremamente ruidoso. Recentemente, diversos experimentos realizados in vivo têm revelado que objetos transportados por motores moleculares ao longo dos microtúbulos apresentam movimento bidirecional. Embora o movimento unidirecional dos motores envolvidos no transporte destes objetos seja bem caracterizado tanto experimentalmente quanto teoricamente, o movimento bidirecional das partículas transportadas pelos motores ainda não é bem entendido. Contudo, acredita-se que este fenômeno seja causado pela cooperatividade dos motores moleculares. Existem na literatura diversos trabalhos que visam descrever o comportamento coletivo de partículas locomovendo-se sobre uma rede unidimensional com interações de volume excluído e taxas de transição assimétricas. Estes modelos são conhecidos como TASEP (Totally asymmetric simple exclusion processes ) ou ASEP (Asymmetric simple exclusion processes ) e fazem parte de uma classe de modelos denominados sistemas difusivos dirigidos_. Embora alguns autores tenham utilizado modelos do tipo ASEP e TASEP para descrever o movimento dos motores moleculares exclusivamente [37], [38], não há ainda nesta visão microscópica, extensões deste modelo para incorporar as partículas cuja dinâmica depende exclusivamente da presença de motores. No presente trabalho propomos um modelo de exclusão, desenvolvido com o intuito de descrever o movimento conjunto de motores moleculares e das partículas carregadas pelos mesmos, as quais por simplicidade denominamos vesículas. Neste modelo, as vesículas não possuem dinâmica própria, ou seja, dependem da interação com os motores moleculares para se movimentarem. Procuramos soluções analíticas para este modelo para o 1 RESUMO 2 caso em que há apenas uma vesícula locomovendo-se sobre a rede. Utilizando o método das matrizes [32], calculamos a velocidade média da vesícula no estado estacionário e analisamos seu comportamento em situações de interesse.
Molecular motors are proteins that transport objects such as vesicles, organelles and macromolecules along the cytoskeletum of cells. For physics, they are very interesting devices because they are able to generate work in an extremely viscous environment. Recently, many in vivo experiments have revealed that objects transported by molecular motors move bidirectionally along microtubules. Although the unidirectional movement of such molecular motors is experimentally and theoretically well characterized, the movement of particles transported by these motors is not well understood yet. However, this fenomenum is believed to be caused by the cooperativity of molecular motors. A great number of works are found in literature, which were formulated to describe the collective behaviour of many particles moving in a one-dimensional lattice with a preferred hop rate and exclusion. These models are known as TASEP (Totally asymmetric simple exclusion processes) or ASEP (Asymmetric simple exclusion processes) and are part of a class of models named _driven di_usive systems_. Although some authors made use of ASEP and TASEP models to describe the movement of molecular motors [37], [38], there is not yet, in this microscopic point of view, extensions of these models capable of incorporate particles which the dynamics depends exclusivaly from the presence of motors. In this work we propose a exclusion model developed to describe the joint movement of molecular motors and particles, generally called vesicles. In this model, vesicles do not have a proper dynamics, that is, they on the interaction with molecular motors to move. We look after analytical solutions of this model when there is only one vesicle moving on the lattice. We use a matrix formulation [32] to obtain the mean velocity of the vesicle and analyse its behaviour in situations of interest.

To achieve the widespread diffusion of autonomous electric buses (AEBs) and thus harness their environmental potential, a broad acceptance of new technology-based mobility concepts must be fostered. Still, there remains little known about the factors determining their acceptance, especially in the combination of vehicles with alternative fuels and autonomous driving modes, as is the case with AEBs. In this study, we first conducted qualitative research to identify relevant factors influencing individual acceptance of autonomously driven electric buses. We then developed a comprehensive research model that was validated through a survey of 268 passengers of an AEB, operated in regular road traffic in Germany. The results indicate that a mix of individual factors, social impacts, and system characteristics determine an individual’s acceptance of AEBs. Notably, it is important that users perceive AEBs, not only as advantageous, but also trustworthy, enjoyable, and in a positive social light. Our research supplements the existing corpora by demonstrating the importance of individual acceptance and incorporating it to derive policy implications.

Dans le développement récent des sciences de réseau, réseaux contraints spatiales sont devenues un objet d'une enquête approfondie. Spatiales des réseaux de contraintes sont intégrées dans l'espace de configuration. Leurs structures et les dynamiques sont influencées par la distance spatiale. Ceci est prouvé par les données empiriques de plus en plus sur des systèmes réels montrant des lois exponentielles ou de distribution d'énergie distance spatiale de liens. Dans cette thèse, nous nous concentrons sur la structure de réseau spatial avec une distribution en loi de puissance spatiale. Plusieurs mécanismes de formation de la structure et de la dynamique de diffusion sur ces réseaux sont pris en considération. D'abord, nous proposons un réseau évolutif construit en l'espace de configuration d'un mécanisme de concurrence entre le degré et les préférences de distance spatiale. Ce mécanisme est décrit par un a^'fc- + (1 — a)^'lL_,1, où ki est le degré du noeud i et rni est la distance spatiale entre les noeuds n et i. En réglant le paramètre a, le réseau peut être fait pour changer en continu à partir du réseau spatiale entraînée (a = 0) pour le réseau sans échelle (a = 1). La structure topologique de notre modèle est comparé aux données empiriques de réseau de courrier électronique avec un bon accord. Sur cette base, nous nous concentrons sur la dynamique de diffusion sur le réseau axé sur spatiale (a — 0). Le premier modèle, nous avons utilisé est fréquemment employée dans l'étude de la propagation de l'épidémie: ['spatiale susceptible-infecté-susceptible (SIS) modèle. Ici, le taux de propagation entre deux noeuds connectés est inversement proportionnelle à leur distance spatiale. Le résultat montre que la diffusion efficace de temps augmente avec l'augmentation de a. L'existence d'seuil épidémique générique est observée, dont la valeur dépend du paramètre a Le seuil épidémique maximum et le ratio minimum fixe de noeuds infectés localiser simultanément dans le intervalle 1.5 < a < 2.Puisque le réseau spatiale axée a bien défini la distance spatiale, ce modèle offre une occasion d'étudier la dynamique de diffusion en utilisant les techniques habituelles de la mécanique statistique. Tout d'abord, compte tenu du fait que la diffusion est anormale en général en raison de l'importante long plage de propagation, nous introduisons un coefficient de diffusion composite qui est la somme de la diffusion d'habitude constante D des lois de la Fick appliqué sur différentes distances de transfert possibles sur le réseau. Comme prévu, ce coefficient composite diminue avec l'augmentation de a. et est une bonne mesure de l'efficacité de la diffusion. Notre seconde approche pour cette diffusion anormale est de calculer le déplacement quadratique moyen (l²) à identifier une constante de diffusion D' et le degré de la anomalousness y avec l'aide de la loi de puissance (l²) = 4D'ty. D' comportements de la même manière que D, i.e.. elle diminue avec l'augmentation de a. y est inférieur à l'unité (subdiffusion) et tend à un (diffusion normale) que a augmente
In the recent development of network sciences, spatial constrained networks have become an object of extensive investigation. Spatial constrained networks are embedded in configuration space. Their structures and dynamics are influenced by spatial distance. This is proved by more and more empirical data on real Systems showing exponential or power laws spatial distance distribution of links. In this dissertation, we focus on the structure of spatial network with power law spatial distribution. Several mechanisms of structure formation and diffusion dynamics on these networks are considered. First we propose an evolutionary network constructed in the configuration space with a competing mechanism between the degree and the spatial distance preferences. This mechanism is described by a ki + (1 — a), where ki is the degree of node i and rni is the spatial distance between nodes n and i. By adjusting parameter a, the network can be made to change continuously from the spatial driven network (a = 0) to the scale-free network (a = 1). The topological structure of our model is compared to the empirical data from email network with good agreement. On this basis, we focus on the diffusion dynamics on spatial driven network (a = 0). The first model we used is frequently employed in the study of epidemie spreading : the spatial susceptible-infected-susceptible (SIS) model. Here the spreading rate between two connected nodes is inversely proportional to their spatial distance. The result shows that the effective spreading time increases with increasing a. The existence of generic epidemic threshold is observed, whose value dépends on parameter a. The maximum épidemic threshold and the minimum stationary ratio of infected nodes simultaneously locate in the interval 1.5 < a < 2. Since the spatial driven network has well defined spatial distance, this model offers an occasion to study the diffusion dynamics by using the usual techniques of statistical mechanics. First, considering the fact that the diffusion is anomalous in general due to the important long-range spreading, we introduce a composite diffusion coefficient which is the sum of the usual diffusion constant D of the Fick's laws applied over different possible transfer distances on the network. As expected, this composite coefficient decreases with increasing a and is a good measure of the efficiency of the diffusion. Our second approach to this anomalous diffusion is to calculate the mean square displacement (l²) to identify a diffusion constant D' and the degree of thé anomalousness y with the help of the power law {l²} = 4D'ty. D' behaviors in the same way as D, i.e., it decreases with increasing a. y is smaller than unity (subdiffusion) and tends to one (normal diffusion) as a increases

La déformation d’une capsule en écoulement dans un canal micro-fluidique est un problème compliqué à simuler numériquement. Nous proposons deux modèles innovants de pilotage de données d’ordre réduit pour simuler le problème spatio-temporel à partir d’une base de données collectée des simulations réalisées avec un modèle d’ordre élevé. L’objectif est de remplacer le modèle numérique haute-fidélité existant par un modèle d’ordre réduit capable de simuler l’évolution de déformation des capsules en écoulement à faible cout en temps et en calcul. Le premier modèle consiste à construire à partir d’un cube de données espace-temps-paramètre un modèle réduit pour simuler la déformation de la microcapsule pour n’importe quelle configuration admissible de paramètres. La prédiction de l’évolution temporelle de la capsule pour une configuration donnée de paramètres et un pas de discrétisation temporelle choisi se fait à l’aide d’un apprentissage sur des variétés du modèle réduit. Le deuxième modèle se base sur l’idée de réécrire le problème sous forme d’un système dynamique d’ordre réduit dans lequel les coefficients spectraux des déplacements et les champs des vitesses sont relies à travers d’un opérateur dynamique à identifier. Pour déterminer ce dernier, nous suggérons l’utilisation d’une approche de décomposition en modes dynamiques. Des validations numériques confirment la fiabilité et stabilité des deux nouveaux modèles par rapport au modèle d’ordre élevé. Une application informatique est également mise au point afin d’explorer l’évolution de déformation des capsules pour toute configuration de paramètres admissibles
The motion of a liquid-filled microcapsule flowing in a microchannel is a complex problem tosimulate. Two innovative reduced-order data-driven models are proposed to replace the Fluid Structure Interaction (FSI) model using a collected database from high-fidelity simulations. The objective is to replace the existing Full Order Model (FOM) with a fast-simulation model that can simulate the capsule deformation in flow at a low cost in terms of time and calculation. The first model consists in building from a space-time-parameter datacube a reduced model to simulate the deformation of the microcapsule for any admissible configuration of parameters. Time evolution of the capsule deformation is treated by identifying the nonlinear low-order manifold of the reduced variables. Then, manifold learning is applied using the Diffuse Approximation (DA) method to predict capsule deformation for a query configuration of parameters and a chosen time discretization. The second model is based on rewriting the FSI model under the form of a reduced-order dynamic system. In this latter, the spectral displacement and velocity coefficients are related through a dynamic operator to be identified. To determine this operator, we suggest the use of a dynamic mode decomposition approach. Numerical validations prove the reliability and stability of the two new models compared to the high order model. A software application has been developed to explore the capsule deformation evolution for any couple of admissible parameters

Penetration of solvents into polymers is sometimes characterized by steep concentration gradients that move into the polymer and last for long times. The behavior of these fronts cannot be explained by standard diffusion equations, even with concentration dependent diffusion coefficients. The addition of stress terms to the diffusive flux can produce such progressive fronts. Model equations are proposed that include solvent flux due to stress gradients in addition to the Fickian flux. The stress in turn obeys an concentration dependent evolution equation.

The model equations are analyzed in the limit of small diffusivity for the problem of penetration into a semi-infinite medium. Provided that the coefficient functions obey certain monotonicity conditions, the solvent concentration profile is shown to have a steep front that progresses into the medium. A formula governing the progression of the front is developed. After the front decays away, the long time behavior of the solution is shown to be a similarity solution. Two techniques for approximating the solvent concentration and the front position are presented. The first approximation method is a series expansion; formulas are given for the initial speed and deceleration of the front. The second approximation method uses a portion of the long time similarity solution to represent the short time solution behind the front.

The addition of a convective term to the solvent flux is shown to raise the possibility of a traveling wave solution. The existence of the traveling wave solution is shown for certain types of coefficient functions. The way the initial front speed evolves onto the traveling wave speed is sketched out.

Stationary, spatially inhomogenous solutions of reaction-diffusion systems are studied in this thesis. These systems appears in biological models based on a Tu- ring's idea of a diffusion driven instability. In the connection, a global behaviour of bifurcation branches of these stationary solutions is analyzed. The thesis in- sists on theory of differential equations and on (particularly topological) methods of nonlinear analysis. The existence, as well as non-compatness in one-dimensional space, of a bifurcation branch of general reaction-diffusion system leading to Tu- ring's efekt is proved. Further, a priori estimates of Thomas model are derived. The results tend to theorem, that forall diffusion coefficient from the preestab- lished set there exists at least one stacionary, spacially nontrivial solution of Tho- mas model.

Indiana University-Purdue University Indianapolis (IUPUI)
Secondary gliomas are an incurable form of brain cancer that are diagnosed in people at a median age of 45 years. Next-generation sequencing has found that secondary glioblastomas have a distinct genetic profile from the more common primary glioblastomas, which are diagnosed in people typically over the age of 60. Over 80% of secondary gliomas contain an IDH1R132H mutation, resulting in neomorphic mutations, which catalyze isocitrate to the oncometabolite D-2-hydroxyglutarate (2-HG) instead of alpha-ketoglutarate (α-KG). As 2-HG accumulates, it induces a hypermethylator phenotype that prevents the cells from differentiating. Acquisition of additional mutations in tumor suppressors such as p53 and/or ATRX likely leads to tumor initiation. Work in the Wells Laboratory has found that loss of the HIPPO adaptor protein AmotL1 is also associated with increased malignancy. AmotL1 inhibits the transcriptional co-activator YAP to suppress both cell growth and migration. To understand the molecular events leading to secondary glioma development, this thesis developed a series of astrocyte cell lines that carry IDH1 and/or p53 mutations. These lines were then studied in 2D and 3D cell culture systems to identify changes that are associated with early secondary glial tumors. Work was also carried out to enable screens for small molecules that can be tested on these cell lines.

Digital technologies radically transform today’s organizations as they permeate both innovation processes and outcomes. While the potential of digital innovations is tremendous, many companies hardly realize the extensive benefits of digital technologies so far. Furthermore, the theoretical understanding of digital innovations is limited since scholars started to challenge the assumptions made in traditional innovation research due to digital technologies’ affordances. Therefore, this thesis seeks to improve the knowledge about digital innovations by analyzing their discovery and diffusion. The discovery of innovations relates to the development of ideas, which can result in new products, processes, or business models. It is essential to investigate companies’ innovation discovery as they often struggle to create innovative ideas and existing theory rarely incorporates the increasing diversity of employees involved in these processes. Papers A and B of this thesis address these issues by examining how Enterprise Social Networks (ESNs) facilitate employees’ innovation discovery. According to Communication Visibility Theory (CVT), the consideration of ESNs is crucial in this regard as they make employees’ everyday communication permanently visible, which provides a basis for acquiring new knowledge. Paper A validates and extends the newly developed CVT. By incorporating individuals employed in diverse contexts, it empirically supports the theory’s external validity. Therefore, different companies can draw on ESNs to foster their innovation discovery, which is made possible through improvements in employees’ meta-knowledge. Besides, the paper reveals that meta-knowledge is not merely formed in the long-run, as indicated by previous research, but in the short-run as well. Interestingly, it also shows that managers can gain more meta-knowledge using ESNs compared to non-managers, which is in contrast with prior literature’s findings. Paper B investigates when employees disclose information in ESNs, which is essential to attain high communication visibility and, in this way, to facilitate the discovery of innovations. To that end, the paper transfers theory on Online Social Networks (OSNs) to the ESN context. It finds that employees’ trusting and risk beliefs are associated with their information disclosure. Additionally, the paper reveals that a company’s group and development culture influence these beliefs, with error aversion culture transmitting the effect of development culture. Innovation diffusion relates to the distribution of a novel product, process, or business model across a group of target users. It is important to better understand the diffusion of digital innovations as companies often lack knowledge about why new offerings are rejected, which limits their chances of counteracting the underlying issues. Furthermore, digital technologies impact the innovation diffusion by blurring industry boundaries and facilitating competition. Papers C and D of this thesis investigate the diffusion of digital innovations in the context of data-driven business models. This context is especially affected by new competition arising across previous boundaries and, thus, necessary to analyze as diverse organizations have high incentives to utilize their data in new ways. Paper C analyzes which dimensions substantially differentiate between distinct data-driven business models. For this purpose, it leverages practitioners’ perceptions of business models obtained from a start-up database. Based on three identified dimensions, the paper creates a taxonomy that classifies the business models into eight ideal-typical categories. The number of business models present in each category provides insights into their diffusion. By offering basic knowledge about the nature of data-driven business models, the paper can be used as a foundation for future research that seeks to dig deeper into this new field and for companies that aim at developing data-driven business models. Paper D investigates how individuals evaluate data-driven services that are offered by highly diverse companies. Based on a qualitative study, the paper shows that individuals’ perception of fit between a service and its provider is crucial for their evaluations. It also reveals the dimensions that influence this perception. Additionally, it explores the consequences that come with a perception of fit. Using these results, the paper offers a new perspective on individuals’ service evaluations, which is vital to the diffusion of the services as well as the associated business models and helps organizations in developing and promoting data-driven services.

Abstracts in English, Afrikaans and Zulu
Literature suggests that human resource practices (HRPs), particularly performance appraisal (PA), contribute to innovation. However, the importance of PA amongst other antecedents to innovation is inadequately described. This leaves human resource managers (HRMs) in the dark on which HRPs they should emphasize. This study contextualises the PA-innovation relationship in South Africa and specifies the importance of PA as a driver of innovation within and across organisations. A cross-sectional survey was employed, acquiring data from a broad cross-section of South African employees and organisations. PA, HRPs and three other antecedents to innovation, and innovation itself, were measured. Across organisations, PA was directly responsible for between 3.8% and 5.7% of the variance in innovation. It was also found that, when PA was combined with other HRPs and other antecedents to innovation, the role of PA was significant, though mostly secondary. Within organisations, the pattern repeated itself with the PAinnovation relationship significant in 30% of organisations, with PA never the dominant driver of innovation in any organisation. The research thus revealed that PA, as an antecedent to innovation, plays a subordinate role, both across employees and within specific organisations. When testing more complex models on the PA-innovation link, the results revealed that the PA-innovation relationship is mediated by work engagement (WE) as well as affective commitment (AC), with WE having the greatest effect. Transformational leadership (TL) and corporate entrepreneurship (CE) moderate the PA-innovation relationship, with TL having the strongest effect and CE having almost no effect. Proactive personality does not moderate the PA-innovation relationship. The results specify the relative importance of PA in general and within specific organisations. The main finding is that PA is not the dominant HRP driving innovation. It also shows that leadership behaviour (TL) more than climate (CE), and WE rather than AC influence the PA innovation relationship. The aforementioned will benefit all stakeholders, particularly HRMs, to focus on appropriate HRPs when trying to enhance innovation at the general employee and organisational level. No previous research has discussed the role of PA as an antecedent to innovation in this degree of detail or contextualised the research as has been done here.
Literatuur suggereer dat menslike hulpbronpraktyke, veral prestasiebeoordeling, bydra tot innovasie. Die belangrikheid van prestasiebeoordeling onder ander antesedente vir innovasie word egter onvoldoende beskryf. Dit laat menslikehulpbronbestuurders in die duister waarop menslike hulpbronpraktyke hulle moet beklemtoon. Hierdie studie kontekstualiseer die prestasiebeoordeling-innovasie-verhouding in Suid-Afrika en spesifiseer die belangrikheid van prestasiebeoordeling as 'n drywer van innovasie binne en oor organisasies. Daar is gebruik gemaak van 'n deursnee-opname met die verkryging van data van 'n breë deursnit van Suid-Afrikaanse werknemers en organisasies. Prestasiebeoordeling, menslike hulpbronpraktyke en drie ander voorvaders vir innovasie en innovasie self is gemeet. Regoor organisasies was prestasiebeoordeling regstreeks verantwoordelik vir tussen 3.8% en 5.7% van die variansie in innovasie. Daar is ook gevind dat, toe prestasiebeoordeling gekombineer is met ander menslike hulpbronpraktyke en ander antesedente vir innovasie, die rol van prestasiebeoordeling belangrik was, hoewel meestal sekondêr. Binne organisasies het die patroon homself herhaal met die prestasiebeoordeling-innovasie-verhouding wat in 30% van die organisasies beduidend was, met prestasiebeoordeling nooit die dominante drywer van innovasie in enige organisasie nie. Die navorsing het dus aan die lig gebring dat prestasiebeoordeling, as 'n voorvader van innovasie, 'n ondergeskikte rol speel, beide oor werknemers en binne spesifieke organisasies. By die toetsing van meer ingewikkelde modelle op die prestasiebeoordeling-innovasie-skakel, het die resultate aan die lig gebring dat die prestasiebeoordeling-innovasie-verhouding bemiddel word deur werksbetrokkenheid sowel as affektiewe toewyding, met die feit dat werksbetrokkenheid die grootste effek het. Transformasionele leierskap en korporatiewe ondernemerskap het die prestasiebeoordeling-innovasie-verhouding gematig, en Transformasionele leierskap het die sterkste effek en korporatiewe ondernemerskap het byna geen effek nie. Proaktiewe persoonlikheid modereer nie die prestasiebeoordeling-innovasie-verhouding nie. Die resultate spesifiseer die relatiewe belang van prestasiebeoordeling in die algemeen en binne spesifieke organisasies. Die belangrikste bevinding is dat prestasiebeoordeling nie die dominante menslike hulpbronpraktyk is wat innovasie dryf nie. Dit wys ook dat leierskapsgedrag meer as klimaat is, en werksbetrokkenheid eerder as affektiewe toewyding die binnovasieverhouding beïnvloed. Bogenoemde sal alle belanghebbendes, veral menslikehulpbronbestuurders, bevoordeel om op toepaslike menslike hulpbronpraktyke te konsentreer as hulle probeer om innovasie op die algemene werknemer- en organisatoriese vlak te bevorder. Geen vorige navorsing het die rol van prestasiebeoordeling as 'n voorkennis vir innovasie in hierdie mate van detail bespreek of die navorsing gekontekstualiseer soos hier gedoen is nie.
Izincwadi zisikisela ukuthi imikhuba yemithombo yabantu, ikakhulu ukutuswa ngomsebenzi, kwenza abantu basungule izinto. Nokho, ukubaluleka kwe-ukutuswa ngomsebenzi phakathi kwezinye izinto kudlula ukusungula izinto okuchazwe ngokungenelea. Lokhu kwenza abaphathi bemithombo yabantu besebumnyameni ngokuthi imaphi ama-imikhuba yemithombo yabantu okufanele bawagcizelele. Lolu cwaningo luhlobanisa ukusungulwa kwezinto ze-ukutuswa ngomsebenzi nobuhlobo eNingizimu Afrika futhi ikhuthaze ngokukhethekile ukubaluleka kweukutuswa ngomsebenzi njengokushukumisa abantu ukuba basungule ngaphakathi nakuzo zonke izinhlangano. Kwasetshenziswa inhlolo-vo kuzo zonke izinhlangano, kwaqoqwa idatha kuzo zonke izingxenye zabasebenzi baseNingizimu Afrika nezinhlangano. I-ukutuswa ngomsebenzi, ama-imikhuba yemithombo yabantu nabanye abasunguli abathathu bezinto, nokusungulwa kwezinto ngokwako kwakalwa. Kuzo zonke izinhlangano, i-ukutuswa ngomsebenzi yayinomthwalo ngokuqondile phakathi kwamaphesenti angu-3.8 no-5.7% zokusungula izinto okuhlukahlukene. Kwatholakala nokuthi, lapho i-ukutuswa ngomsebenzi ihlanganiswa namanye ama-imikhuba yemithombo yabantu nezinye izinhlangano ezisungula izinto, indima ye-ukutuswa ngomsebenzi yayibalulekile, nakuba ingeyesibili. Phakathi nezinhlangano, umkhuba wawuziphindaphinda ekusunguleni kwe-ukutuswa ngomsebenzi nobuhlobo nezinhlangano ezingamaphesenti angu-30, i-ukutuswa ngomsebenzi yayingashukumisi ukusungula izinto kunoma iyiphi inhlangano. Ngakho, ucwaningo lwembula ukuthi i-ukutuswa ngomsebenzi, njengento esungulayo, inendima ebalulekile, kokubili kubasebenzi nasezinhlanganweni ezithile. Lapho kuhlolwa izimo eziyinkimbinkimbi kakhulu ekuhlobaneni nokusungula kwe-ukutuswa ngomsebenzi, imiphumela yembula ukuthi ukusungula kwe-ukutuswa ngomsebenzi kuhlobene nokusebenza kanye nokuzibophezela okuphumelelayo, i-kuhlobene nokusebenza inomthelela omkhulu kakhulu. Abaholi bezinguquko nabaphathi bezinkampani bayakulinganisa ubuhlobo bokusungula ne-ukutuswa ngomsebenzi, i-abaholi bezinguquko inomthelela omkhulu kakhulu futhi i-nabaphathi bezinkampani ingenawo umthelela. Ubuntu obuhle abulinganiseli ubuhlobo bokusungula kwe-ukutuswa ngomsebenzi. Imiphumela ibonisa ukubaluleka kwe-ukutuswa ngomsebenzi phakathi ezinhlanganweni ezithile. Okwatholakala ukuthi i-ukutuswa ngomsebenzi ayiyona into eyinhloko eshukumisa ukusungula kwe-imikhuba yemithombo yabantu. Ibuye ibonise ukuziphatha kwabaholi ngaphezu kwesimo sezulu, ne-kuhlobene nokusebenza kunethonya le-nokuzibophezela okuphumelelayo ebuhlotsheni bokusungula kwe-ukutuswa ngomsebenzi. Lokho okuphawulwe ngenhla kuyozuzisa wonke ama-stakeholder, ikakhulu ama-abaphathi bemithombo yabantu, ukuze agxile kuma-imikhuba yemithombo yabantu afanele lapho ezama ukukhuthaza abasebenzi abavamile nezinhlangano ukuba basungule. Alukho ucwaningo lwangaphambili oluke lwaxoxa ngendima ye-ukutuswa ngomsebenzi njengesungula izinto kuleli zinga elinemininingwane noma ibeke ucwaningo ngokunembile njengoba kwenziwe lapha.
Business Management
D.B.L.