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Non-explosive pre-supernova feedback in the colibre model of galaxy formation
Get PDFWe present the implementation and testing of a subgrid non-explosive pre-supernova (NEPS) feedback module for the colibre model of galaxy formation. The NEPS module incorporates three key physical processes sourced by young, massive stars that act immediately following star formation: momentum injection from stellar winds and radiation pressure, and thermal energy from photoheating in H ii regions. The age- and metallicity-dependent energy and momentum budgets are derived from bpass stellar population models and are coupled self-consistently to the local gas properties. We test the model using a suite of smoothed particle hydrodynamics simulations of isolated, unstable gaseous discs at various numerical resolutions (gas particle masses in the range ). We find that the NEPS module successfully regulates star formation by providing pressure support that prevents catastrophic gas collapse. This regulation improves the numerical convergence of star formation rates and disc structure. In our model, feedback from H ii regions is the dominant regulatory mechanism. Furthermore, we demonstrate a crucial synergy with subsequent supernova feedback; NEPS feedback pre-processes the interstellar medium, creating a more homogeneous environment that moderates the effect of explosive feedback from supernova events. Our NEPS module thus provides a physically motivated and numerically robust framework that mitigates resolution-dependent artefacts and promotes self-regulated galaxy growth
Investigating the Efficacy of Topologically Derived Time Series for Flare Forecasting. II. XGBoost Model
Get PDFSolar flares are a primary driver of space weather, and forecasting their occurrence remains a significant challenge. This paper presents a novel flare prediction model based on topologically derived photospheric magnetic parameters. We employ the ARTop framework to compute the time-dependent input rates of magnetic winding and helicity across >105 active region observations, decomposing them into current-carrying and potential components to reduce sensitivity to optical flow methods. An XGBoost machine learning model is trained on these time series, alongside engineered features including rolling statistics, kurtosis, and flare history, to predict the probability of ≥M1.0 class flares within the next 24 hr. The model demonstrates strong performance on a validation set, with a true skill statistic (TSS) of 0.804 for once-daily operational region forecasts. When applied to a fully independent dataset, the model achieves a TSS of 0.524. A SHAP analysis confirms the model’s physical interpretability, identifying flare history and accumulated current-carrying winding and helicity as the most important features. The main challenges identified are false positives arising from active regions with frequent C-class flaring and systematic errors via projection effects when active regions are near the limb. Excluding limb-affected data yields no improvement in the holdout set TSS (0.521 versus 0.524), due to the overall decreased number of flares. However, our per-region analysis indicates that mitigating these projection effects is crucial for future operational deployment. This work establishes magnetic topology, particularly its current-carrying components, as a highly effective and physically meaningful set of predictors for solar flare forecasting
Suzuki-Miyaura cross-couplings from carboxylic acids via in situ acyl fluoride electrophiles
Get PDFAcyl fluorides have been previously shown to be competent electrophiles in the generation of ketones via Suzuki-Miyaura Cross-Couplings. However, such methodologies rely on isolated, pre-formed acyl fluorides which hampers the scope and flexibility of these approaches. In addition many acyl fluorides are unstable under ambient conditions and they suffer from instability during synthesis, isolation, or storage. Herein we report the use of an in situ generation of acyl fluorides in combination with Suzuki-Miyaura Cross-Coupling to generate di-aryl ketones. This allows the direct conversion of ubiquitous carboxylic acids to highly valuable ketones. The developed methodology was also found to be applicable to a range of aromatic and heteroaromatic carboxylic acids, affording an increased reaction scope compared to contemporary approaches
Bones of St Francis of Assisi go on display for the first time – here’s why it took 800 years
No full textThe Oxford Handbook of Leadership, Followership, and Identity
No full textLeadership and followership are not just roles, but dynamic identities shaped by complex identity construction and deconstruction processes that define who leads, who follows, and how individuals navigate managerial transitions and changes in their roles.In The Oxford Handbook of Leadership, Followership, and Identity, Olga Epitropaki and Ronit Kark bring together prominent scholars to delve into the evolving field of leader and follower identity. They explore how our self-perceptions as leaders and followers can shape personal, team, and organizational outcomes, as well as how these identities evolve over time. Chapters highlight intrapersonal identity processes and identity development across diverse contexts; how relational and contextual factors influence leader and follower identities; the challenges of navigating multiple identities and identity tensions; intergroup leadership; cultural influences on identity integration; the role of vision communication in shaping collective identity; and the need for leadership development to extend beyond formal roles. Over the course of the book, chapter authors cover emerging themes, such as temporality, context, relational and collective elements, intersectionality, and critical perspectives, that capture the complexity of leader-follower identity processes and open new pathways for theoretical and empirical research.By synthesizing cutting-edge research and offering forward-looking perspectives, the Handbook serves as a resource for leadership and organizational scholars and a springboard for innovative approaches to leadership development. Whether one's goal is to gain a deeper understanding of leadership and followership identity processes or to apply a novel approach to leadership development, this volume offers an essential roadmap for navigating the complexities of leadership, followership, and identity in modern organizations
On ‘Caring Against’: A feminist, political and spatial account of how care builds and sustains resistance
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Fostering an environment for social entrepreneurship: a comparative analysis across economic development levels
Get PDFSocial entrepreneurship has been lauded for its positive contributions to global economic and social development goals. Yet, how and in what ways varying institutional environments and economic development levels have spurred social entrepreneurial ventures remains a highly debated concept. It remains unclear whether (or not) social ventures are most likely to emerge within developing nations with weak and ineffective institutional structures or from developed nations with more established and supportive institutional mechanisms. Therefore, this study responds to this debate and provides comparative evidence on how varying national economic development levels constrain or enable social entrepreneurship behavior. The study combines data from the Global Entrepreneurship Monitor, the World Development Indicators, the Index of Economic Freedom, and the World Governance Indicators to develop a multi-level mixed-effects model. It uses a sample of 124,642 individuals from 59 (9 factor-, 27 efficiency-, and 23 innovation-driven) countries. The results indicate a positive association with informal institutional mechanisms influencing global social venture formation. However, disparate observations on how some formal institutional factors influence social venture across economic development levels were observed, raising essential questions about formal institutional support mechanisms' influence
Cardinality and Utilitarianism through social interactions
No full textWe provide axioms that relate the preferences of each group in a society to the preferences of the subgroups contained in them. These axioms yield cardinal utility indices for each individual and a representation of group preferences as the group-dependent weighted sum of the utility indices of the members of that group. We show that these weights are group-independent whenever one additional axiom, and a mild linear independence assumption are satisfied
(Almost) Perfect Discrete Iterative Load Balancing
Get PDFWe consider discrete, iterative load balancing via matchings on arbitrary graphs. Initially each node holds a certain number of tokens, defining the load of the node, and the objective is to redistribute the tokens such that eventually each node has approximately the same number of tokens. We present results for a general class of simple local balancing schemes where the tokens are balanced via matchings. In each round the process averages the tokens of any two matched nodes. If the sum of their tokens is odd, the node to receive the one excess token is selected at random. Our class covers three popular models: in the matching model a new matching is generated randomly in each round, in the balancing circuit model a fixed sequence of matchings is applied periodically, and in the asynchronous model the load is balanced over a randomly chosen edge.We measure the quality of a load vector by its discrepancy, defined as the difference between the maximum and minimum load across all nodes. As our main result we show that with high probability our discrete balancing scheme reaches a discrepancy of 3 in a number of rounds which asymptotically matches the spectral bound for continuous load balancing with fractional load.This result improves and tightens a long line of previous works, by not only achieving a small constant discrepancy (instead of a non-explicit, large constant) but also holding for arbitrary instead of regular graphs. The result also demonstrates that in the general model we consider, discrete load balancing is no harder than continuous load balancing
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