Electroresistance in non-tunnelling ferroelectric junctions

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2018, Tutor: Ignasi FinaFerroelectric materials are of potential interest for their integration in memristive devices. Polarization switching in ferroelectric thin film junctions might lead to a change of the electronic band diagram of the device, which can result in important changes of resistance. This effect is known as electroresistance. Electroresistance in 12.2, 24.3 and 36.5 nm BTO thin films junctions is investigated. It is observed that electroresistance decreases with thickness. In addition, ferroelectric characterization allows to conclude that switchable ferroelectric polarization also decreases with thickness. Thus, we conclude that electroresistance is intimately linked to the ferroelectric switching process

Building balance to build resilience: An empirical study on the neighbourhood balance policy of Rotterdam's resilience strategy

The rise in urban stresses has prompted the need for preparedness of urban areas to face precarious circumstances. Consequently, the concept of urban resilience has grown in popularity not only to tackle sudden shocks but also to face long-lasting socio-economic tensions. To implement the arrangements for resilience policy, literature suggests that social factors govern the resilience of urban areas. Communities in which the residents work together and have common goals have a stronger willingness to cooperate. To this end, social cohesion has been proven to be significant for subsistence in the event of a catastrophe. Cohesive communities protect residents against threats, care of others during hardships, and ultimately promote community resilience.Balanced neighbourhood policies aim to strengthen the cohesion between citizens, communities, and social institutions departing from the assumption that social mix fosters social cohesion. Their goal is to increase the social mix of specific areas to avoid the clustering and segregation of disadvantaged households to, as a result, promote resilient actions. There is, however, literature that suggests that the anticipated effects are rather inconclusive and usually not achieved. Instead, balanced neighbourhood policies would promote segregation by forcing the displacement of groups of residents.The issue arises whether balanced neighbourhoods trigger resilient actions that are pivotal in resilient communities. In other words, does neighbourhood balance increase resilient action of neighbourhood residents? We took a cross-sectional confirmatory approach to understand the social mechanism that triggers resilient action in balanced neighbourhoods based on Partial Least Squares—Structural Equation Modelling (PLS-SEM) and spatial econometrics. To this end, the research tests the assumptions on which the municipality of Rotterdam grounds their Resilience Strategy's balanced neighbourhood policy, the Woonvisie, using a 2019 public survey on social development. Rotterdam's definition of a balanced neighbourhood is defined from a set of conditions for the amount of houses in different house price segments. Therefore, the tested model is based on the grounds that geographically connected people become affected by their neighbourhood's balance to promote resilient action. As such, we use the willingness to help friends and neighbours to characterise informal support as resilient action. Here we show that balanced neighbourhoods are associated with less informal support: the higher the balance, the fewer residents are willing to help their friends and neighbours.The results indicate that social cohesion is the social mechanism that triggers help between friends and relatives and fully acts as the mechanism for resilient actions triggered by the balance in a neighbourhood. From the multiple combinations of houses in different house price segments that the definition of balanced neighbourhoods allows, we distinguish two associations. On one hand, house price distributions which foment a reduction in polarisation (more middle-priced houses) are negatively associated with social cohesion. On the other hand, balanced neighbourhoods which foment polarisation (more low- and high-priced houses) are positively associated with social cohesion. This indicates that our results are in line with Putnam’s homophily principle, i.e. ‘birds of a feather flock together’. This outcome is opposite to the policy discourse of governments in favour of balanced neighbourhoods, including the municipality of Rotterdam, that mixed neighbourhoods foster social cohesion and therefore resilient action.The testing of the theory is complemented in two ways. First, we show that social cohesion and informal support are not constrained by administrative boundaries, so the social perceptions and actions in nearby neighbourhoods affects the level of the other neighbourhoods. Second, we found no moderating effect of factors related to the demographics and the built environment that can promote or deter social interactions, and thus are aspects of what can be considered a resilient neighbourhood.The analysis also shows that Rotterdam's definition of balance allows multiple and dispersed combinations of the amount of houses in each price segment, which can result in counterintuitive conceptions of balance. In addition, the results show apparently contradicting results of the relationship between balance and social cohesion depending on whether the distribution foments house price polarisation. As a result, we argue that the definition is under-specified and can be misleading. Finally, only 2.1% of the possible balance distributions yielded an acceptable goodness-of-fit of our model. This could be indicative that the model needs to be reevaluated. We found that neighbourhood ethnic heterogeneity and house type heterogeneity are directly associated to social cohesion and informal support, respectively. Future research should elaborate on the theory on which the model is grounded and create coherence to the empirical relationships identified. In contrast, the few fitting distributions could otherwise indicate that that social cohesion and informal support cannot be explained by the balance in a neighbourhood and that the policy should be reevaluated. Under this second interpretation, the study has uncovered which are the balance distributions for the city that can actually show the alleged effects of balance.Based on these findings, a policy advice is formulated. If the objective is to increase social cohesion and resilient actions, we discourage the municipality of Rotterdam to approach this by building balanced neighbourhoods. Nevertheless, we have seen that building social cohesion is a way to build social resilience, so recently developed city programs focused on the development of neighbourhood organisations, which not only provide a space for social cohesion but also to collect and share resources directly, are a step forward from the Woonvisie.Engineering and Policy Analysi