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Gregor Ramien

Publications and source records attributed to Gregor Ramien.

3 recordsLinked to original sources

In-context learning to predict critical transitions in dynamical systems

Critical transitions - abrupt, often irreversible changes in system dynamics - arise across human and natural systems, often with catastrophic consequences. Real-world observations of such shifts remain scarce, preventing the development of reliable early warning systems. Conventional statistical and spectral indicators, such as increasing variance, tend to fail under realistic conditions of limited data and correlated noise, whereas existing deep learning classifiers do not extrapolate beyond their training data distribution. In this work, we introduce TipPFN, an in-context learning (ICL) framework that uses a prior-data fitted network to infer a system's proximity to a critical transition. Trained on our novel synthetic data generator, which is based on canonical bifurcation scenarios coupled to diverse, randomized stochastic dynamics, TipPFN flexibly capitalizes on contexts of various sizes, complexity and dimensionalities. We demonstrate robust, state-of-the-art early detection of critical transitions in previously unseen tipping regimes, sim-to-real examples, and real-world observations in both ICL and zero-shot settings.

cs.LG

CausalDynamics: A large-scale benchmark for structural discovery of dynamical causal models

Causal discovery for dynamical systems poses a major challenge in fields where active interventions are infeasible. Most methods used to investigate these systems and their associated benchmarks are tailored to deterministic, low-dimensional and weakly nonlinear time-series data. To address these limitations, we present CausalDynamics, a large-scale benchmark and extensible data generation framework to advance the structural discovery of dynamical causal models. Our benchmark consists of true causal graphs derived from thousands of both linearly and nonlinearly coupled ordinary and stochastic differential equations as well as two idealized climate models. We perform a comprehensive evaluation of state-of-the-art causal discovery algorithms for graph reconstruction on systems with noisy, confounded, and lagged dynamics. CausalDynamics consists of a plug-and-play, build-your-own coupling workflow that enables the construction of a hierarchy of physical systems. We anticipate that our framework will facilitate the development of robust causal discovery algorithms that are broadly applicable across domains while addressing their unique challenges. We provide a user-friendly implementation and documentation on https://kausable.github.io/CausalDynamics.

cs.LG

X-ray-frequency modulation via periodic switching of an external magnetic field

Single x-ray photons can be resonantly scattered and stored with the help of suitable transitions in the atomic nucleus. Here, we investigate theoretically means of mechanical-free modulation for the frequency spectra of such x-ray photons via periodic switching of an external magnetic field. We show that periodically switching on and off an external magnetic field generating hyperfine splitting of the nuclear transition leads to the generation of equidistant narrow sidebands of the resonantly scattered response. This frequency-comb-like structure depends on the magnitude and orientation of the applied magnetic field and on the switching period. An analytical approach for the characterization of the comblike frequency spectrum is presented. The feasibility of the external control on the frequency modulation of the x-ray response is discussed in view of possible applications in high-resolution spectroscopy or quantum technology.

quant-ph