8,334 research outputs found
Time Domain Mapping of Spin Torque Oscillator Effective Energy
Stochastic dynamics of spin torque oscillators (STOs) can be described in
terms of magnetization drift and diffusion over a current-dependent effective
energy surface given by the Fokker-Planck equation. Here we present a method
that directly probes this effective energy surface via time-resolved
measurements of the microwave voltage generated by a STO. We show that the
effective energy approach provides a simple recipe for predicting spectral line
widths and line shapes near the generation threshold. Our time domain technique
also accurately measures the field-like component of spin torque in a wide
range of the voltage bias values.Comment: 5 pages, 3 figures. Supplement included: 7 pages, 6 figure
Modeling resilience and sustainability in ancient agricultural systems
The reasons why people adopt unsustainable agricultural practices, and the ultimate environmental implications of those practices, remain incompletely understood in the present world. Archaeology, however, offers unique datasets on coincident cultural and ecological change, and their social and environmental effects. This article applies concepts derived from ecological resilience thinking to assess the sustainability of agricultural practices as a result of long-term interactions between political, economic, and environmental systems. Using the urban center of Gordion, in central Turkey, as a case study, it is possible to identify mismatched social and ecological processes on temporal, spatial, and organizational scales, which help to resolve thresholds of resilience. Results of this analysis implicate temporal and spatial mismatches as a cause for local environmental degradation, and increasing extralocal economic pressures as an ultimate cause for the adoption of unsustainable land-use practices. This analysis suggests that a research approach that integrates environmental archaeology with a resilience perspective has considerable potential for explicating regional patterns of agricultural change and environmental degradation in the past
Learning dynamics on invariant measures using PDE-constrained optimization
We extend the methodology in [Yang et al., 2023] to learn autonomous
continuous-time dynamical systems from invariant measures. The highlight of our
approach is to reformulate the inverse problem of learning ODEs or SDEs from
data as a PDE-constrained optimization problem. This shift in perspective
allows us to learn from slowly sampled inference trajectories and perform
uncertainty quantification for the forecasted dynamics. Our approach also
yields a forward model with better stability than direct trajectory simulation
in certain situations. We present numerical results for the Van der Pol
oscillator and the Lorenz-63 system, together with real-world applications to
Hall-effect thruster dynamics and temperature prediction, to demonstrate the
effectiveness of the proposed approach.Comment: This article may be downloaded for personal use only. Any other use
requires prior permission of the author and AIP Publishing. This article
appeared in Chaos: An Interdisciplinary Journal of Nonlinear Science, Volume
33, Issue 6, June 2023, and may be found at https://doi.org/10.1063/5.014967
Solidarity at Work:Concepts, levels and challenges
Solidarity is not a unified phenomenon with unchanging qualities; it partakes of moral, political and performative elements that are underpinned and reinforced by a shared work context, an organizational infrastructure and an institutional frame which together create distinctive path dependencies in solidarity across different forms of capitalism. Neo-liberalism has challenged these path dependencies by changing the material conditions and the ideological terrain, by heightening the diversity of the workforce, by restructuring the institutional context. However, this is not the end of solidarity and the article addresses the question of what sort of solidarities are now emerging and how.status: publishe
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