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The contact hypothesis re-evaluated
This paper evaluates the state of contact hypothesis research from a policy perspective. Building on Pettigrew and Tropp's (2006) influential meta-analysis, we assemble all intergroup contact studies that feature random assignment and delayed outcome measures, of which there are 27 in total, nearly two-thirds of which were published following the original review. We find the evidence from this updated dataset to be consistent with Pettigrew and Tropp's (2006) conclusion that contact “typically reduces prejudice.” At the same time, our meta-analysis suggests that contact's effects vary, with interventions directed at ethnic or racial prejudice generating substantially weaker effects. Moreover, our inventory of relevant studies reveals important gaps, most notably the absence of studies addressing adults' racial or ethnic prejudices, an important limitation for both theory and policy. We also call attention to the lack of research that systematically investigates the scope conditions suggested by Allport (1954) under which contact is most influential. We conclude that these gaps in contact research must be addressed empirically before this hypothesis can reliably guide policy.
Journal Article
Is Voting Habit Forming? New Evidence from Experiments and Regression Discontinuities
Field experiments and regression discontinuity designs test whether voting is habit forming by examining whether a random shock to turnout in one election affects participation in subsequent elections. We contribute to this literature by offering a vast amount of new statistical evidence on the long-term consequences of random and quasi-random inducements to vote. The behavior of millions of voters confirms the persistence of voter turnout and calls attention to theoretically meaningful nuances in the development and expression of voting habits. We suggest that individuals become habituated to voting in particular types of elections. The degree of persistence appears to vary by electoral context and by the attributes of those who comply with an initial inducement to vote.
Journal Article
Global threats to human water security and river biodiversity
Protecting the world’s freshwater resources requires diagnosing threats over a broad range of scales, from global to local. Here we present the first worldwide synthesis to jointly consider human and biodiversity perspectives on water security using a spatial framework that quantifies multiple stressors and accounts for downstream impacts. We find that nearly 80% of the world’s population is exposed to high levels of threat to water security. Massive investment in water technology enables rich nations to offset high stressor levels without remedying their underlying causes, whereas less wealthy nations remain vulnerable. A similar lack of precautionary investment jeopardizes biodiversity, with habitats associated with 65% of continental discharge classified as moderately to highly threatened. The cumulative threat framework offers a tool for prioritizing policy and management responses to this crisis, and underscores the necessity of limiting threats at their source instead of through costly remediation of symptoms in order to assure global water security for both humans and freshwater biodiversity.
Dual threat to river biodiversity and water security
Access to fresh water is essential for all life forms, but water security for humans and biodiversity are often seen as competing priorities. A new analysis of the threats to the world's rivers breaks new ground by accounting for a broad array of stressors and their downstream effects, from both human and biodiversity perspectives. A subsequent analysis of investments in water resources offers insights into the sources of global disparities in human water security that separate rich from poor. The authors conclude that rivers are in a state of crisis, and that nearly 80% of humanity lives in areas where threat levels are relatively high. River-dwelling species face similarly great challenges around the world. Achieving a sustainable solution to these problems, the authors say, will require creative solutions that jointly address water security for humans and biodiversity, and that treat underlying causes rather than merely symptoms.
Water security affects human wellbeing both directly and indirectly, through its effects on biodiversity. Here, a global map has been generated that shows threats to both direct and indirect water security from a full range of potential stressors. Technological investments have also been incorporated. The map shows that nearly 80% of the world's population is exposed to high levels of threat to water security. Investment enables rich nations to offset high stressor levels, but less wealthy nations remain vulnerable.
Journal Article
Bayesian and Markov chain Monte Carlo methods for identifying nonlinear systems in the presence of uncertainty
In this paper, the authors outline the general principles behind an approach to Bayesian system identification and highlight the benefits of adopting a Bayesian framework when attempting to identify models of nonlinear dynamical systems in the presence of uncertainty. It is then described how, through a summary of some key algorithms, many of the potential difficulties associated with a Bayesian approach can be overcome through the use of Markov chain Monte Carlo (MCMC) methods. The paper concludes with a case study, where an MCMC algorithm is used to facilitate the Bayesian system identification of a nonlinear dynamical system from experimentally observed acceleration time histories.
Journal Article
Directed evolution of an efficient and thermostable PET depolymerase
The recent discovery of
Is
PETase, a hydrolytic enzyme that can deconstruct poly(ethylene terephthalate) (PET), has sparked great interest in biocatalytic approaches to recycle plastics. Realization of commercial use will require the development of robust engineered enzymes that meet the demands of industrial processes. Although rationally engineered PETases have been described, enzymes that have been experimentally optimized via directed evolution have not previously been reported. Here, we describe an automated, high-throughput directed evolution platform for engineering polymer degrading enzymes. Applying catalytic activity at elevated temperatures as a primary selection pressure, a thermostable
Is
PETase variant (HotPETase,
T
m
= 82.5 °C) was engineered that can operate at the glass transition temperature of PET. HotPETase can depolymerize semicrystalline PET more rapidly than previously reported PETases and can selectively deconstruct the PET component of a laminated multimaterial. Structural analysis of HotPETase reveals interesting features that have emerged to improve thermotolerance and catalytic performance. Our study establishes laboratory evolution as a platform for engineering useful plastic degrading enzymes.
Enzymes for poly(ethylene terephthalate) (PET) deconstruction are of interest for plastics recycling, but reports on their directed evolution are missing. Now, an automated, high-throughput directed evolution platform is described, affording HotPETase that effectively achieves depolymerization above the glass transition temperature of PET.
Journal Article