Phase-field-crystal models for condensed matter dynamics on atomic length and diffusive time scales: an overview

Here, we review the basic concepts and applications of the phase-field-crystal (PFC) method, which is one of the latest simulation methodologies in materials science for problems, where atomic- and microscales are tightly coupled. The PFC method operates on atomic length and diffusive time scales, and thus constitutes a computationally efficient alternative to molecular simulation methods. Its intense development in materials science started fairly recently following the work by Elder et al. [Phys. Rev. Lett. 88 (2002), p. 245701]. Since these initial studies, dynamical density functional theory and thermodynamic concepts have been linked to the PFC approach to serve as further theoretical fundaments for the latter. In this review, we summarize these methodological development steps as well as the most important applications of the PFC method with a special focus on the interaction of development steps taken in hard and soft matter physics, respectively. Doing so, we hope to present today's state of the art in PFC modelling as well as the potential, which might still arise from this method in physics and materials science in the nearby future.Comment: 95 pages, 48 figure

Stochastic Hysteresis and Resonance in a Kinetic Ising System

We study hysteresis for a two-dimensional, spin-1/2, nearest-neighbor, kinetic Ising ferromagnet in an oscillating field, using Monte Carlo simulations and analytical theory. Attention is focused on small systems and weak field amplitudes at a temperature below $T_{c}$. For these restricted parameters, the magnetization switches through random nucleation of a single droplet of spins aligned with the applied field. We analyze the stochastic hysteresis observed in this parameter regime, using time-dependent nucleation theory and the theory of variable-rate Markov processes. The theory enables us to accurately predict the results of extensive Monte Carlo simulations, without the use of any adjustable parameters. The stochastic response is qualitatively different from what is observed, either in mean-field models or in simulations of larger spatially extended systems. We consider the frequency dependence of the probability density for the hysteresis-loop area and show that its average slowly crosses over to a logarithmic decay with frequency and amplitude for asymptotically low frequencies. Both the average loop area and the residence-time distributions for the magnetization show evidence of stochastic resonance. We also demonstrate a connection between the residence-time distributions and the power spectral densities of the magnetization time series. In addition to their significance for the interpretation of recent experiments in condensed-matter physics, including studies of switching in ferromagnetic and ferroelectric nanoparticles and ultrathin films, our results are relevant to the general theory of periodically driven arrays of coupled, bistable systems with stochastic noise.Comment: 35 pages. Submitted to Phys. Rev. E Minor revisions to the text and updated reference

A global experiment on motivating social distancing during the COVID-19 pandemic

Finding communication strategies that effectively motivate social distancing continues to be a global public health priority during the COVID-19 pandemic. This cross-country, preregistered experiment (n = 25,718 from 89 countries) tested hypotheses concerning generalizable positive and negative outcomes of social distancing messages that promoted personal agency and reflective choices (i.e., an autonomy-supportive message) or were restrictive and shaming (i.e., a controlling message) compared with no message at all. Results partially supported experimental hypotheses in that the controlling message increased controlled motivation (a poorly internalized form of motivation relying on shame, guilt, and fear of social consequences) relative to no message. On the other hand, the autonomy-supportive message lowered feelings of defiance compared with the controlling message, but the controlling message did not differ from receiving no message at all. Unexpectedly, messages did not influence autonomous motivation (a highly internalized form of motivation relying on one’s core values) or behavioral intentions. Results supported hypothesized associations between people’s existing autonomous and controlled motivations and self-reported behavioral intentions to engage in social distancing. Controlled motivation was associated with more defiance and less long-term behavioral intention to engage in social distancing, whereas autonomous motivation was associated with less defiance and more short- and long-term intentions to social distance. Overall, this work highlights the potential harm of using shaming and pressuring language in public health communication, with implications for the current and future global health challenges

A global experiment on motivating social distancing during the COVID-19 pandemic

Finding communication strategies that effectively motivate social distancing continues to be a global public health priority during the COVID-19 pandemic. This cross-country, preregistered experiment (n = 25,718 from 89 countries) tested hypotheses concerning generalizable positive and negative outcomes of social distancing messages that promoted personal agency and reflective choices (i.e., an autonomy-supportive message) or were restrictive and shaming (i.e. a controlling message) compared to no message at all. Results partially supported experimental hypotheses in that the controlling message increased controlled motivation (a poorly-internalized form of motivation relying on shame, guilt, and fear of social consequences) relative to no message. On the other hand, the autonomy-supportive message lowered feelings of defiance compared to the controlling message, but the controlling message did not differ from receiving no message at all. Unexpectedly, messages did not influence autonomous motivation (a highly-internalized form of motivation relying on one’s core values) or behavioral intentions. Results supported hypothesized associations between people’s existing autonomous and controlled motivations and self-reported behavioral intentions to engage in social distancing: Controlled motivation was associated with more defiance and less long-term behavioral intentions to engage in social distancing, whereas autonomous motivation was associated with less defiance and more short- and long-term intentions to social distance. Overall, this work highlights the potential harm of using shaming and pressuring language in public health communication, with implications for the current and future global health challenges

A global experiment on motivating social distancing during the COVID-19 pandemic

Significance Communicating in ways that motivate engagement in social distancing remains a critical global public health priority during the COVID-19 pandemic. This study tested motivational qualities of messages about social distancing (those that promoted choice and agency vs. those that were forceful and shaming) in 25,718 people in 89 countries. The autonomy-supportive message decreased feelings of defying social distancing recommendations relative to the controlling message, and the controlling message increased controlled motivation, a less effective form of motivation, relative to no message. Message type did not impact intentions to socially distance, but people’s existing motivations were related to intentions. Findings were generalizable across a geographically diverse sample and may inform public health communication strategies in this and future global health emergencies. Abstract Finding communication strategies that effectively motivate social distancing continues to be a global public health priority during the COVID-19 pandemic. This cross-country, preregistered experiment (n = 25,718 from 89 countries) tested hypotheses concerning generalizable positive and negative outcomes of social distancing messages that promoted personal agency and reflective choices (i.e., an autonomy-supportive message) or were restrictive and shaming (i.e., a controlling message) compared with no message at all. Results partially supported experimental hypotheses in that the controlling message increased controlled motivation (a poorly internalized form of motivation relying on shame, guilt, and fear of social consequences) relative to no message. On the other hand, the autonomy-supportive message lowered feelings of defiance compared with the controlling message, but the controlling message did not differ from receiving no message at all. Unexpectedly, messages did not influence autonomous motivation (a highly internalized form of motivation relying on one’s core values) or behavioral intentions. Results supported hypothesized associations between people’s existing autonomous and controlled motivations and self-reported behavioral intentions to engage in social distancing. Controlled motivation was associated with more defiance and less long-term behavioral intention to engage in social distancing, whereas autonomous motivation was associated with less defiance and more short- and long-term intentions to social distance. Overall, this work highlights the potential harm of using shaming and pressuring language in public health communication, with implications for the current and future global health challenges

The evolution of urban and regional planning in Canada: 1900-1960

Urban and regional planning is now accepted as a legitimate function of government. But the evolution of Canadian planning from its inception at the turn of.the century to its new-found status as an objective technical exercise has been a profoundly complex process involving questions about the very nature of society. This thesis is an attempt to trace the development of the theory and practice of planning from its controversial beginnings at the turn of the century to its final acceptance as a necessary and desirable function of the state. At the beginning of the century it became clear that the rapid pace of urbanization and the capitalist institutions of private property and unregulated private markets were in serious conflict. The new urban, industrial order that accompanied capital accumulation was plagued by interdependences and interactions which made the unrestricted use of property an antiquated and dangerous illusion threatening the physical health of the population, the efficiency of the urban system, and the social stability of the entire society. Canadians responded to this conflict in three distinct and somewhat contradictory ways. One approach which was advocated by agrarian radicals was to implement reforms in Canadian society in order to revitalize rural life and reverse the undesirable trend of urbanization. The second approach, which was advocated by urban liberals, was to accept urbanization as both desirable and inexorable and to accommodate it by initiating limited reforms while still preserving the basic features of capitalism. The third response, advocated by urban radicals, was to accept urbanization as inexorable and to restructure capitalist institutions which were inimical to the sorts of government planning they thought was necessary to manage the new urban order. Urban and regional planning was considered as essential by all these groups. After going through several initial stages of development, a comprehensive body of planning theory which appealed to all three groups was formulated by leading Canadian planners such as Adams. This theory integrated the aesthetic concerns of city beautiful planning, the efficiency concerns of American city planning, and the equity concerns of British town planning. The theory envisaged a strong role for the state in controlling property and providing housing. By the twenties, the consensus that had formed around this theory of planning collapsed due to a gradual amelioration of urban problems and an overt confrontation between liberals and urban and agrarian radicals. During the twenties a new, more conservative theory of planning developed which emphasized the protection of private property and the provision of public infrastructure to accommodate private accumulation. Planners became allied with real estate interests who were eager to use zoning and other powers of the state to their advantage. With the collapse of the economy in the thirties, the latent ideological conflicts which had been submerged in the twenties reappeared with renewed vitality. The urban and agrarian radicals joined forces to form a socialist party dedicated to eradicating capitalism and replacing it with a planned economy. Liberals were forced to formulate a new system of both managing the crisis and preserving capitalism. Gradually they developed a new consensus that was based on the three principles of Keynesian stabilization policies, social welfare and sectoral planning for those areas of the economy plagued by market failures. Housing and land were defined as one of the sectors of the economy affected by market failures. Major government reports defined a new postwar system of urban and regional planning to mitigate these failures in land and housing markets. The reports were highly critical of the type of planning existing in the twenties, and proposed a new more comprehensive system of planning and of controls over property. The urban liberals, however, who were the dominant group, were apprehensive about the increased role of the state envisaged in these reports. Consequently, they only partially implemented the recommended reforms. Urban and regional planning, although strengthened, was ultimately subordinated to the interests of private markets and property. It again became a passive system of regulation providing necessary services to accommodate private expansion and regulations to enhance property rights. Nonetheless, its strengthened position ensured that the worst features of development were eliminated. The tendency of liberal planning to shift back and forth between more aggressive intervention during times of crisis and very passive intervention during times of stability has meant that, because of the long lag times between the emergence of crisis and the creation of plans and institutions capable of managing the crisis, Canadian planning has been strongest after the crisis has already subsided or when it has changed form. Consequently, the ability to plan has been highest when the need to plan has been lowest. One question raised by the thesis is why the more passive liberal approach to planning emerged as the dominant one.. It is argued that this is due, in large part, to Canada's unique character of economic development and class structure. Unlike countries such as Britain which developed more socialist modes of planning, urbanization in Canada was accompanied by a rapid expansion in agriculture and staple industries. Consequently, the Canadian response to development was logically divided between urban and rural concerns. Canada's industrial capitalist class and working class which were both promoting more aggressive urban planning were too weak to have much influence. The more powerful agrarian radicals and mercantile capitalists were able to direct attention away from the emerging urban problems to rural and resource issues which directly affected them. In the end, the urban liberals were successful in resolving the conflict between urbanization and capitalist institutions. Limited acceptance of urban and regional planning allowed for the successful management of urban problems within the framework of capitalist institutions. Whether it will continue to be successful in doing this only time will tell.Applied Science, Faculty ofCommunity and Regional Planning (SCARP), School ofGraduat

Maternal diet and aging alter the epigenetic control of a promoter–enhancer interaction at the Hnf4a gene in rat pancreatic islets

Environmental factors interact with the genome throughout life to determine gene expression and, consequently, tissue function and disease risk. One such factor that is known to play an important role in determining long-term metabolic health is diet during critical periods of development. Epigenetic regulation of gene expression has been implicated in mediating these programming effects of early diet. The precise epigenetic mechanisms that underlie these effects remain largely unknown. Here, we show that the transcription factor Hnf4a, which has been implicated in the etiology of type 2 diabetes (T2D), is epigenetically regulated by maternal diet and aging in rat islets. Transcriptional activity of Hnf4a in islets is restricted to the distal P2 promoter through its open chromatin configuration and an islet-specific interaction between the P2 promoter and a downstream enhancer. Exposure to suboptimal nutrition during early development leads to epigenetic silencing at the enhancer region, which weakens the P2 promoter–enhancer interaction and results in a permanent reduction in Hnf4a expression. Aging leads to progressive epigenetic silencing of the entire Hnf4a locus in islets, an effect that is more pronounced in rats exposed to a poor maternal diet. Our findings provide evidence for environmentally induced epigenetic changes at the Hnf4a enhancer that alter its interaction with the P2 promoter, and consequently determine T2D risk. We therefore propose that environmentally induced changes in promoter-enhancer interactions represent a fundamental epigenetic mechanism by which nutrition and aging can influence long-term health