A Process Model of Risk Communication: The Case of Global Climate Change

The authors describe a survey of public media use as it relates to different stages of awareness and concern regarding risk issues

The Effects of High Liquid Water Content on Thunderstorm Charging

Charge transfer to a riming graupel target during interactions with ice crystals has been investigated in the laboratory. When liquid water contents sufficiently high to cause wet growth are achieved, the charge transfer falls to values which are insignificant to thunderstorm electrification. The implications of this null result to a recent analysis of thunderstorm-charging processes by Wiliams et al. (1991) are discussed

Extreme radio-wave scattering associated with hot stars

We use data on extreme radio scintillation to demonstrate that this phenomenon is associated with hot stars in the solar neighbourhood. The ionized gas responsible for the scattering is found at distances up to 1.75pc from the host star, and on average must comprise 1.E5 distinct structures per star. We detect azimuthal velocities of the plasma, relative to the host star, up to 9.7 km/s, consistent with warm gas expanding at the sound speed. The circumstellar plasma structures that we infer are similar in several respects to the cometary knots seen in the Helix, and in other planetary nebulae. There the ionized gas appears as a skin around tiny molecular clumps. Our analysis suggests that molecular clumps are ubiquitous circumstellar features, unrelated to the evolutionary state of the star. The total mass in such clumps is comparable to the stellar mass.Comment: 9 pages, 1 figure, to appear in Ap

Cosmological Radiation Hydrodynamics with ENZO

We describe an extension of the cosmological hydrodynamics code ENZO to include the self-consistent transport of ionizing radiation modeled in the flux-limited diffusion approximation. A novel feature of our algorithm is a coupled implicit solution of radiation transport, ionization kinetics, and gas photoheating, making the timestepping for this portion of the calculation resolution independent. The implicit system is coupled to the explicit cosmological hydrodynamics through operator splitting and solved with scalable multigrid methods. We summarize the numerical method, present a verification test on cosmological Stromgren spheres, and then apply it to the problem of cosmological hydrogen reionization.Comment: 14 pages, 3 figures, to appear in Recent Directions in Astrophysical Quantitative Spectroscopy and Radiation Hydrodynamics, Ed. I. Hubeny, American Institute of Physics (2009

High-Energy Astrophysics in the 2020s and Beyond

With each passing decade, we gain new appreciation for the dynamic, connected, and often violent nature of the Universe. This reality necessarily places the study of high-energy processes at the very heart of modern astrophysics. This White Paper illustrates the central role of high-energy astrophysics to some of the most pressing astrophysical problems of our time, the formation/evolution of galaxies, the origin of the heavy elements, star and planet formation, the emergence of life on exoplanets, and the search for new physics. We also highlight the new connections that are growing between astrophysicists and plasma physicists. We end with a discussion of the challenges that must be addressed to realize the potential of these connections, including the need for integrated planning across physics and astronomy programs in multiple agencies, and the need to foster the creativity and career aspirations of individual scientists in this era of large projects.Comment: Astro2020 White Paper submissio

Investigations into ion transport properties of polymerized ionic liquids and related materials

The body of work on polymerized ionic liquids has been growing rapidly in recent years as researchers expand the synthesis space to achieve novel membrane materials with high conductivity, excellent mechanical stability, and high transference number. Despite progress in identifying specific new polymers and useful properties, there has been limited agreement over the mechanism for ion transport in these materials. It is essential that we resolve said mechanism for polymerized-ionic-liquid conduction, with the goal of streamlining future material design. Molecular dynamics is an excellent tool for analyzing local coordination behavior, ion-hopping pathways, and other phenomena of length- and time-scales that are currently inaccessible to direct experimental observation. Ion transport is seen to proceed via a "climbing the ladder" mechanism involving the formation and breaking of ion-association pairs with, on average, four polymerized ions from two polymer chains. This results in a link between ion-association lifetime and diffusivity for chemically similar polymerized ionic liquids, a feature that distinguishes polymerized ionic liquids from a broad class of polymer electrolytes and low fragility ionomers. This is also shown to be the case for a set of backbone-polymerized ionic liquids, when compared to a chemically similar pendent-polymerized ionic liquid. This is particularly interesting because the pendent architectural motif proves to have significantly higher reversibility of ion-hopping events. The application of design rules inspired by this research has already led to the experimental discovery of highly decoupled polymerized ionic liquids with excellent conductivity at ambient temperature. Parametric simulation studies of poly(vinylimidazolium) polymerized ionic liquids and counterion variants have revealed a decoupling of ion mobility from polymer segmental dynamics. Small counterions are generally more decoupled, but results show that size is not the sole arbiter. For this set of different chemical components, encompassed by the anionic study, ion-association relaxation time, rather than lifetime, was proven to better correlate with diffusivity. Similar physics is observed between polymerized ionic liquids and salt-doped polymerized zwitterions for the population of mobile ions whose polymerized counter-charge is located on the end of a monomeric pendant. However, the cage-relaxation timescale appears to correlate better with diffusivity for the opposite ion in such materials.Chemical Engineerin

Cyclopropanation Catalyzed by Osmium Porphyrin Complexes

Cyclopropanation of alkenes can be accomplished catalytically2 or stoichiometrically.3 Catalytic systems typically use a diazo reagent as the carbene source and a metal-containing mediator which forms a postulated metal carbene intermediate. Transfer of the carbene fragment from the metal to an alkene produces the cyclopropane product. Despite the wide variety of catalytic cyclopropanation systems, the putative carbene complex has never been isolated or observed in a catalytic system. This is somewhat surprising since the second category of cyclopropanation reactions involves the stoichiometric reaction of isolated car bene complexes with an alkene to form a cyclopropane. None of the isolated carbene complexes show catalytic cyclopropanation activity. Several years ago Callot demonstrated that rhodium porphyrins catalytically cyclopropanated a variety of alkenes in the presence of ethyl diazoacetate.4 Kodadek and co-workers have expanded this work and have attempted to prepare synthetically useful enantioselective catalysts for the formation of cyclopropanes.5 Their approach has been to use rhodium complexes with optically active porphyrins to induce chirality into the product. A similar approach was used for a variety of non-porphyrin copper catalysts.6 Kodadek has shown that the carbon-bound diazonium complex [(TTP)RhC(H)(C02Et)(N2W is an intermediate in the catalytic cyclopropanation of styrene with ethyl diazoacetate.7•8 In addition, kinetic studies suggest that the formation of a rhodium carbene complex is at least partially rate limiting.8 However, this carbene complex has not been isolated or directly observed. We report herein the use of osmium porphyrins as stereoselective cyclopropanation catalysts using ethyl diazoacetate with a variety of alkenes. In addition, our studies show that an isolable carbene complex ((TTP)Os=CHC02Et) is capable of catalytically and stoichiometrically cyclopropanating styrene

Geological and 40Ar/39Ar geochronological constraints on the timing of quartz vein formation in Meguma Group lode-gold deposits, Nova Scotia

The results of geological and 40Ar/39Ar geochronological investigations of several gold districts hosted by the Meguma Group are presented. Observations at both the macro- (deposit to ore zone) and micro- (hand sample to thin section) scale indicate that quartz vein formation followed major Acadian folding and metamorphism (ca. 400 ±10 Ma) and was broadly coincident with mafic-felsic magmatism at ca. 370 Ma. 40Ar/39Ar analyses of vein-fill mica and amphibole from the Beaver Dam, Moose River, Fifteen Mile Stream, Upper Seal Harbour and Caribou deposits indicate ages of ca. 380 Ma to ca. 362 Ma. The age data are interpreted to reflect discrete hydrothermal events with rapid cooling following crystallization of vein constituents. The age data do not reflect either variable amounts of resetting by later granitic intrusions or diachronous cooling. Genetic models that interpret the generation of the auriferous quartz veins as either before or during major Acadian folding are considered to be inconsistent with the present results. Instead, a model is favored that interprets quartz vein formation in the context of continued transpression of the Meguma Terrane following regional folding and metamorphism. RÉSUMÉ On présente les résultats d'études géologiques et géochronologiques [40Ar/39Ar] effectuées dans plusieurs districts aurifères au sein du Groupe de Meguma. Des observations tant macroscopiques (du gite à la zone de minéral) que microscopiques (de l'échantillon à la lame mince) indiquent que la formation des veines de quartz suivit un métamorphisme et un plissement majeurs acadiens (env. 400 ± 10 Ma) et coiincida d'une facon générale avec unmagmatisme mafique à felsique vers 370 Ma. Des analyses 40Ar/39Ar effectuées sur des micas et des amphiboles de remplissages de veine provenant des gites de Beaver Dam, Moose River, Fifteen Mile Stream, Upper Seal Harbour et Caribou révèlent des âges aux environs de 380 à 362 Ma. On interprète ces données d 'âge comme le reflet d'épisodes hydrothèrmaux distincts avec un refroidissement rapide suite à la cristallisation des constituants filoniens. Ces données ne reflètent ni un degré variable de remise à ziro par des intrusions granitiques ultérieures, ni un refroidissement diachrone. On considere que les modèles genetiques interprétant la formation des veines de quartz auriferes comme precedent ou ayant eu lieu pendant le plissement majeur acadien, sont en contradiction avec les resultats actuels. En leur lieu, on favorise un modèle qui interprète la formation des veines de quartz dans le contexte d'une transpression continue de la Lanière de Méguma à la suite d'un plissement et d'un métamorphisme régionaux. [Traduit par le journal

Grassroots Ecology: Plant-Microbe-Soil Interactions as Drivers of Plant Community Structure and Dynamics

A growing body of research on plant–microbe interactions in soil is contributing to the development of a new, microbially based perspective on plant community ecology. Soil-dwelling microorganisms are diverse, and interactions with plants vary with respect to specificity, environmental heterogeneity, and fitness impact. Two microbial processes that may exert key influences on plant community structure and dynamics are microbial mediation of niche differentiation in resource use and feedback dynamics between the plant and soil community. The niche differentiation hypothesis is based on observations that soil nutrients occur in different chemical forms, that different enzymes are required for plant access to these nutrients, and that soil microorganisms are a major source of these enzymes. We predict that plant nutrient partitioning arises from differential associations of plant species with microbes able to access different nutrient pools. Feedback dynamics result from changes in the soil community generated by the specificity of response in plant–microbe interactions. We suggest that positive feedback between plants and soil microbes plays a central role in early successional communities, while negative feedback contributes both to species replacements and to diversification in later successional communities. We further suggest that plant–microbe interactions in the soil are an important organizing force for large-scale spatial gradients in species richness. The relative balance of positive feedback (a homogenizing force) and negative feedback (a diversifying force) may contribute to observed latitudinal (and altitudinal) diversity patterns. Empirical tests of these ideas are needed, but a microbially based perspective for plant ecology promises to contribute to our understanding of long-standing issues in ecology, and to reveal new areas of future research