A primer on noise-induced transitions in applied dynamical systems

Noise plays a fundamental role in a wide variety of physical and biological dynamical systems. It can arise from an external forcing or due to random dynamics internal to the system. It is well established that even weak noise can result in large behavioral changes such as transitions between or escapes from quasi-stable states. These transitions can correspond to critical events such as failures or extinctions that make them essential phenomena to understand and quantify, despite the fact that their occurrence is rare. This article will provide an overview of the theory underlying the dynamics of rare events for stochastic models along with some example applications

Diffusion and Decoherence of Squarks and Quarks During the Electroweak Phase Transition

To estimate the diffusion constant $D$ of particles in a plasma, we develop a method that is based on the mean free path $\lambda$ for scatterings with momentum transfer $q >~ T$. Using this method, we estimate $\lambda$ and $D$ for squarks and quarks during the electroweak phase transition. Assuming that Debye and magnetic screening lengths provide suitable infrared cutoffs, our calculations yield $\lambda <~ 18/T$ and $D <~ 5/T$ for both squarks and quarks. Our estimate of $\lambda$ suggests that suppressions of charge transport due to decoherence of these strongly interacting particles during the electroweak phase transition are not severe and that these particles may contribute significantly to electroweak baryogenesis.Comment: 11 pages. Expanded discussion of our method and approximations, reference adde

Changing Income Inequality and Immigration in Canada 1980-1995

While there is a general consensus that income inequality has increased in most developed countries over the last two decades, the analytical focus has been at the national scale. However, these increases in inequality have not been uniform across different segments of society, either in terms of social group or geographic region. In particular, the high levels of immigration to metropolitan Canada have contributed to growing inequality. Using micro-level data on household income from the 1981,1986,1991 and 1996 censuses, this paper identifies the role of immigration and its differential impact on metropolitan and non-metropolitan areas. The impacts accelerated during the first half of the 1990s when immigration remained high yet the economy slowed. The evidence suggests that the overall impact of immigration is a relatively short-run phenomenon as recent immigrants take time to adjust to the labour market. If recent immigrants are excluded, inequality is still increasing, but at a slower rate, especially in the largest metropolitan areas.income inequality; immigration

Geographic Dimensions of Aging in Canada 1991-2001

Although population aging at the national level has received much attention, its geographical dimensions have not. Here we explore the demographic processes which underlie population aging at the provincial and metropolitan scale for the periods 1991-1996 and 1996-2001. A demographic accounting framework is proposed which differentiates between the effects of aging-in-place and net migration on population aging. We also examine the relationships between the various measures of aging and social and economic characteristics of metropolitan areas over the two periods. We demonstrate that the path of population aging is susceptible to social and economic context; in particular, the struggles of the British Columbian economy in the second half of the decade and the deteriorating economies of older resources based communities are associated with increases in population aging over and above the general aging taking place in Canadian society.population aging; geographic differences

Communication-Wear: User Feedback as Part of a Co-Design Process

Communication-Wear is a clothing concept that augments the mobile phone by enabling expressive messages to be exchanged remotely, by conveying a sense of touch, and presence. It proposes to synthesise conventions and cultures of fashion with those of mobile communications, where there are shared attributes in terms of communication and expression. Using garment prototypes as research probes as part of an on-going iterative co-design process, we endeavoured to mobilise participants’ tacit knowledge in order to gauge user perceptions on touch communication in a lab-based trial. The aim of this study was to determine whether established sensory associations people have with the tactile qualities of textiles could be used as signs and metaphors for experiences, moods, social interactions and gestures, related to interpersonal touch. The findings are used to inspire new design ideas for textile actuators for use in touch communication in successive iterations

What is a Tree Worth? An Appraisal of the University of Pennsylvania’s Tree Population

In 2018, the University of Pennsylvania received a level 2 arboretum accreditation. This new status provides incentive for establishing rigorous tree protection protocols and policies. To preserve and protect a healthy urban forest, it is necessary to develop a plant health care and maintenance program, which can be a costly process. By appraising Penn’s campus tree population, and by determining the monetary benefits trees provide through their environmental and ecosystem services, we can advocate for a tree care budget that is consistent with the value of the asset. We used methods outlined in the Council for Tree and Landscape Appraisal’s (CTLA) Guide to Plant Appraisal to appraise a sample of Penn’s campus trees. This process involved collecting data on the size, species, condition, and location of trees around campus. Additionally, an estimate of the environmental and ecosystem services rendered by these trees was generated using the i-Tree Eco program. The appraised value for Penn’s campus trees was $12.6 million dollars and the environmental benefits totaled approximately$161,000 dollars. The figure for environmental benefits is likely an underestimate, because we only included the minimum data required to run the i-Tree model. In the future, including interpretative signage on or around trees that mentions their appraised value and environmental benefits, may assist in educating the Penn and greater Philadelphia communities about the importance of trees in urban environments

Quantitative functional interrelations within the cis-regulatory system of the S. purpuratus Endo16 gene

Embryonic expression of the Endo16 gene of Strongylocentrotus purpuratus is controlled by interactions with at least 13 different DNA-binding factors. These interactions occur within a cis-regulatory domain that extends about 2300 bp upstream from the transcription start site. A recent functional characterization of this domain reveals six different subregions, or cis-regulatory modules, each of which displays a specific regulatory subfunction when linked with the basal promoter and in some cases various other modules (C.-H. Yuh and E. Davidson (1996) Development 122, 1069-1082). In the present work, we analyzed quantitative time-course measurements of the CAT enzyme output of embryos bearing expression constructs controlled by various Endo16 regulatory modules, either singly or in combination. Three of these modules function positively in that, in isolation, each is capable of promoting expression in vegetal plate and adjacent cell lineages, though with different temporal profiles of activity. Models for the mode of interaction of the three positive modules with one another were tested by assuming mathematical relations that would generate, from the measured single module time courses, the experimentally observed profiles of activity obtained when the relevant modules are physically linked in the same construct. The generated and observed time functions were compared, and the differences were minimized by least squares adjustment of a scale parameter. When the modules were tested in context of the endogenous promoter region, one of the positive modules (A) was found to increase the output of the others (B and G), by a constant factor. In contrast, a solution in which the time-course data of modules A and B are multiplied by one another was required for the interrelations of the positive modules when a minimal SV40 promoter was used. One interpretation is that, in this construct, each module independently stimulates the basal transcription complex. We used a similar approach to analyze the repressive activity of the three Endo16 cis-regulatory modules that act negatively in controlling spatial expression. The evidence obtained confirms that the repressive modules act only by affecting the output of module A (C.-H. Yuh and E. Davidson (1996) Development 122, 1069-1082). A new hierarchical model of the cis-regulatory system was formulated in which module A plays a central integrating role, and which also implies specific functions for certain DNA-binding sites within the basal promoter fragment of the gene. Additional kinetic experiments were then carried out, and key aspects of the model were confirmed