Characterization of Infrared Dark Clouds -- NH3_3 Observations of an Absorption-contrast Selected IRDC Sample

Despite increasing research in massive star formation, little is known about its earliest stages. Infrared Dark Clouds (IRDCs) are cold, dense and massive enough to harbour the sites of future high-mass star formation. But up to now, mainly small samples have been observed and analysed. To understand the physical conditions during the early stages of high-mass star formation, it is necessary to learn more about the physical conditions and stability in relatively unevolved IRDCs. Thus, for characterising IRDCs studies of large samples are needed. We investigate a complete sample of 218 northern hemisphere high-contrast IRDCs using the ammonia (1,1)- and (2,2)-inversion transitions. We detected ammonia (1,1)-inversion transition lines in 109 of our IRDC candidates. Using the data we were able to study the physical conditions within the star-forming regions statistically. We compared them with the conditions in more evolved regions which have been observed in the same fashion as our sample sources. Our results show that IRDCs have, on average, rotation temperatures of 15 K, are turbulent (with line width FWHMs around 2 km s$^{-1}$), have ammonia column densities on the order of $10^{14}$ cm$^{-2}$ and molecular hydrogen column densities on the order of $10^{22}$ cm$^{-2}$. Their virial masses are between 100 and a few 1000 M$_\odot$. The comparison of bulk kinetic and potential energies indicate that the sources are close to virial equilibrium. IRDCs are on average cooler and less turbulent than a comparison sample of high-mass protostellar objects, and have lower ammonia column densities. Virial parameters indicate that the majority of IRDCs are currently stable, but are expected to collapse in the future.Comment: 21 pages, 11 figures, 7 tables. Paper accepted for publication in Astronomy & Astrophysic

Asymptotic linking of volume-preserving actions of Rk{\mathbb R}^k

We extend V. Arnold's theory of asymptotic linking for two volume preserving flows on a domain in ${\mathbb R}^3$ and $S^3$ to volume preserving actions of ${\mathbb R}^k$ and ${\mathbb R}^\ell$ on certain domains in ${\mathbb R}^n$ and also to linking of a volume preserving action of ${\mathbb R}^k$ with a closed oriented singular $\ell$-dimensional submanifold in ${\mathbb R}^n$, where $n=k+\ell+1$. We also extend the Biot-Savart formula to higher dimensions.Comment: 32 pages. We extend Arnol'd's asymptotic linking to actions of {\mathbb^R}^k and {\mathbb^R}^\ell. The only change in this version is that several latex errors and internal references were corrected. The MSC 2020 classification was correcte

Toward Citizen Centricity: Leveraging the Citizens Academy to Foster Inclusive, Sustainable, and Generative Civic Engagement in Midland, MI

This service learning project aims to utilize positive psychology research to foster inclusive, sustainable, and generative civic engagement among residents of Midland, Michigan. We conceptualize civic engagement as an outgrowth of social capital, and we leverage the constructs of mattering, fairness, belonging, and bridging to offer positive interventions aimed at increasing Midland’s social capital. Specifically, we propose several changes to evolve the city government’s existing educational civic leadership program called the Citizens Academy. First, we suggest adjusting the academy’s recruitment process to expand access and inclusion by increasing the number and diversity of participants. Second, we introduce a more participatory and citizen-centered approach to the program content that builds on Midland’s four strategic pillars as a guiding framework. We offer four positive psychology-based exercises to be interwoven into the Citizens Academy curriculum: Strengths and Values, Community Exploration Guide, Citizen-to-Citizen Coaching, and Storytelling. Third, we recommend a Civic Engagement Scale as a simple tool to measure initial outcomes. It is our hope that this service learning project will serve not only as an initial catalyst for Midland’s goal of increasing civic engagement, but as a model for other cities and communities looking to utilize the science of positive psychology to effect large-scale change

The signature of competition in ecomorphological traits across the avian radiation

Competition for shared resources represents a fundamental driver of biological diversity. However, the tempo and mode of phenotypic evolution in deep-time has been predominantly investigated using trait evolutionary models which assume that lineages evolve independently from each other. Consequently, the role of species interactions in driving macroevolutionary dynamics remains poorly understood. Here, we quantify the prevalence for signatures of competition between related species in the evolution of ecomorphological traits across the bird radiation. We find that mechanistic trait models accounting for the effect of species interactions on phenotypic divergence provide the best fit for the data on at least one trait axis in 27 out of 59 clades ranging between 21 and 195 species. Where it occurs, the signature of competition generally coincides with positive species diversity-dependence, driven by the accumulation of lineages with similar ecologies, and we find scarce evidence for trait-dependent or negative diversity-dependent phenotypic evolution. Overall, our results suggest that the footprint of interspecific competition is often eroded in long-term patterns of phenotypic diversification, and that other selection pressures may predominantly shape ecomorphological diversity among extant species at macroevolutionary scales