1,720,984 research outputs found
An investigation into the evolution of hierarchy and its consequences for evolvability
No full textThis thesis is concerned with the evolution of hierarchical modules in a model of gene regulation, and the consequences thereof for evolvability. Developmental processes map genotypes to phenotypes, and translate random variation at the genetic level into biased, selectable variation at the phenotypic level. These developmental processes are themselves subject to evolution by natural selection and it might be the case that natural selection favours developmental architectures that facilitate phenotypic variation that is adaptive and enhances evolvability. One manner of developmental organisation that has inspired much interest is modular hierarchy. Such hierarchy - where one gene directs many others - has the potential to be very important to evolvability because it effectively rescales the variability of phenotypes, enabling natural selection to search combinations of modules rather than combinations of individual genes. However, the conditions where natural selection favours hierarchical organisation and the conditions where its consequences enable such rescaling are not well understood. Considering a developmental model based on a recurrent regulatory process, we describe conditions where natural selection favours the evolution of single-layer hierarchical modular structures, where independent ‘switch’ genes direct independent subsets of genes. We show that these structures increase evolvability by rescaling the genetic neighbourhood of phenotypes, from combinations of genes to combinations of modules, and that this makes high-fitness phenotypes more accessible to natural selection. This improved evolvability enables a micro-evolutionary process to better exploit a changing or static modular environment so long as sufficient long-term variation is maintained. We then investigate the underlying cause of the evolution of hierarchy. Interestingly, we find that the observable increase in evolvability (in particular, the ability to rescale the variability of phenotypes) is not required for natural selection to favour hierarchy in this model. Rather, hierarchy evolves due to a selective pressure for efficient phenotypic expression and because it is an efficient organisation for increasing the expression of many genes given limited regulatory connections. Thereby, we show that - in some cases - the causes and consequences of developmental hierarchy are not the same. That is, hierarchy evolves - and it increases evolvabilty - but increased evolvability need not be the reason it was favoured by selection
Ghent
No full textMedium: engravingMedium: etchingprintssigned."Ghent" [1990.2016.000.000], Goodall, Edward, Nash, FrederickArtist and Role: Goodall, Edward,Artist and Role: Nash, Frederick, ArtistExtent: comp. 7.3 x 11.
Unravelling the dynamics behind the urban morphology of port-cities using a LUTI model based on cellular automata
No full textThe urban morphology is characterised by self-organisation where interactions of multiple agents produce emerging patterns on the urban form. Port-urban relationship added to the complexity of port cities’ urban form. Most urban cellular automata (CA) models simulate land-use evolution through transition rules representing multi-factored local interactions. However, calibration of CA-based urban land use and transport interaction (LUTI) models often utilise manual methods due to complexity of the process. This limits insights on urban interactions to a few explored settlements and prevents applications for planning and assessment of transport policies in other contexts. This paper, therefore, addresses three main points. The paper (i) demonstrates an improved method for the calibration of CA-based LUTI models, (ii) contributes to a better understanding of the urban dynamics in port city systems by quantifying generalizable interactions from a wide range of port-urban settlements, and (iii) illustrates how the use of these interactions in a simulation model can allow long-term impact predictions of planning interventions.These were done by formulating a model in a similar structure as a neural network model to enable automatic calibration using an application of the gradient-descent algorithm. The model was then used to quantify the dynamics between land-use, geographic, and transport factors in 46 port-based and 10 non-port settlements across Great Britain, thus enabling cross-sectional analysis. Cluster analysis of the calibrated interactions in the study areas was conducted to examine the variations of these interactions. This produced two main groups. In the first group, consisting larger settlements, connections between ports and other urban activities were weaker than in the second group which consisted of smaller port-settlements. Overall, the findings of the research are consistent with existing evidence in the port-cities literature but go further in quantifying the interaction between urban agents within port-urban systems of various sizes and types. These quantified interactions will enable planners to better predict the longer-term consequences of their interventions
On the consistency of urban cellular automata models based on hexagonal and square cells
No full textCellular automata have found extensive applications in the modelling of urban systems. Calculations in cellular automata models are based on cell centroids and therefore cellular automata models are sensitive to the choices of cell size and shape. While the effect of cell size for urban simulation has been studied, discussions on the effect of cell shape on urban cellular automata models have been limited. Applications in other fields suggest there are advantages of using hexagonal cells over square cells, yet most urban cellular automata models use square cells. Using connectivity indices from graph theory, experiments in this study compared models based on hexagonal and square cells to examine the potential advantage of hexagonal cells in urban cellular automata models. This paper finds that simulation results from the model with hexagonal cells are more consistent and concludes that hexagonal cells would increase the robustness of model simulation.</p
Modelling urban dynamics as driving forces of land use change in port cities
No full textThe urban environment is a complex system where general urban morphology patterns emerge from local interactions of many human and natural agents. The nature of these individual interactions is difficult to examine from empirical data due to their auto-correlation and to path-dependence in the evolution of urban systems. For the same reasons, calibrations of urban land-use and transport interaction models based on cellular automata (CA) often rely on manual methods. However, this paper shows that a gradient-descent algorithm can be used to calibrate an agent-based CA model of urban areas, wherein cells are characterised by the levels of each activity type they host rather than by categorical states representing only their dominant land-use. This automated process allows efficient calibration of the model for multiple urban settlements, enabling cross-sectional analysis of whether an observed relationship is unique to a settlement due to its path-dependence, or has similarities with results from other settlements. This paper uses the model to investigate the nature of urban dynamics within port-cities by examining the interactions between geographic features, land-use, and transport in 46 port-based settlements and 10 non-port settlements across Great Britain. It shows that port activities had most pronounced effects on smaller settlements, with urban dynamics in larger settlements affected little by the presence of port. There were though variations in urban dynamics between larger settlements with respect to the effects of their retail and manufacturing activities on other land-use. The automated calibration of agent-based urban CA models in this paper enabled the quantification of these interactions in multiple settlements, providing the ability to look beyond the uniqueness of individual case studies to find general patterns of interaction. This study therefore provides important insights into the driving forces of land-use changes in port-cities which could help facilitate future sustainable transport and land use development
Measuring urban dynamics in port-cities using an agent-based cellular automata land-use and transport interaction model
No full textThe urban environment is a complex system where general urban morphology patterns emerge from the local interactions of many agents. Examination on these interactions are crucial to enable successful transport and urban planning. While cellular automata (CA) models are suitable for modelling this self-organisation behaviour, measuring individual interactions from empirical data is still complicated due to their auto-correlation and to path-dependence in urban systems evolution. Due to this, manual methods are more often used in the calibration of urban land-use and transport interaction (LUTI) models based on CA, limiting the results to a few explored settlements. This paper therefore presents a method for applying the gradient-descent algorithm with momentum to calibrate an agent-based LUTI-CA model by representing the model as an optimisation problem. This process allowed efficient calibration for 46 port-related settlements and 10 non-port settlements across Great Britain, enabling cross-sectional analysis of whether observed relationships are unique to a study area due to its path-dependence, or if they have similarities with results from other study areas.We found unique characteristics of urban dynamics separating port from non-port settlements in smaller urban systems, while the distinctions between the two groups were less prominent in larger settlements. However, there were variations in urban dynamics between larger settlements with respect to the effects of their services and manufacturing activities on other land-uses. The automated calibration of agent-based urban CA models in this paper enabled the quantification of these urban dynamics in multiple settlements, providing the ability to look beyond the uniqueness of individual case studies to find general patterns of interaction. This paper therefore provides improvement in the calibration of LUTI models based on CA and contributes to the better understanding of the dynamics between port and urban systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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