570 research outputs found
Ionization of Rydberg atoms embedded in an ultracold plasma
We have studied the behavior of cold Rydberg atoms embedded in an ultracold
plasma. We demonstrate that even deeply bound Rydberg atoms are completely
ionized in such an environment, due to electron collisions. Using a fast pulse
extraction of the electrons from the plasma we found that the number of excess
positive charges, which is directly related to the electron temperature Te, is
not strongly affected by the ionization of the Rydberg atoms. Assuming a
Michie-King equilibrium distribution, in analogy with globular star cluster
dynamics, we estimate Te. Without concluding on heating or cooling of the
plasma by the Rydberg atoms, we discuss the range for changing the plasma
temperature by adding Rydberg atoms.Comment: To be published in P.R.
Environmental Principles in U.S. and Canadian Law
Published as Chapter 29 in Principles of Environmental Law, Ludwig Krämer & Emanuela Orlando, eds.https://digitalcommons.law.buffalo.edu/book_sections/1369/thumbnail.jp
ML-Based Teaching Systems: A Conceptual Framework
As the shortage of skilled workers continues to be a pressing issue, exacerbated by demographic change, it is becoming a critical challenge for organizations to preserve the knowledge of retiring experts and to pass it on to novices. While this knowledge transfer has traditionally taken place through personal interaction, it lacks scalability and requires significant resources and time. IT-based teaching systems have addressed this scalability issue, but their development is still tedious and time-consuming. In this work, we investigate the potential of machine learning (ML) models to facilitate knowledge transfer in an organizational context, leading to more cost-effective IT-based teaching systems. Through a systematic literature review, we examine key concepts, themes, and dimensions to better understand and design ML-based teaching systems. To do so, we capture and consolidate the capabilities of ML models in IT-based teaching systems, inductively analyze relevant concepts in this context, and determine their interrelationships. We present our findings in the form of a review of the key concepts, themes, and dimensions to understand and inform on ML-based teaching systems. Building on these results, our work contributes to research on computer-supported cooperative work by conceptualizing how ML-based teaching systems can preserve expert knowledge and facilitate its transfer from SMEs to human novices. In this way, we shed light on this emerging subfield of human-computer interaction and serve to build an interdisciplinary research agenda
Constrained-Transport Magnetohydrodynamics with Adaptive-Mesh-Refinement in CHARM
We present the implementation of a three-dimensional, second order accurate
Godunov-type algorithm for magneto-hydrodynamic (MHD), in the
adaptive-mesh-refinement (AMR) cosmological code {\tt CHARM}. The algorithm is
based on the full 12-solve spatially unsplit Corner-Transport-Upwind (CTU)
scheme. The fluid quantities are cell-centered and are updated using the
Piecewise-Parabolic-Method (PPM), while the magnetic field variables are
face-centered and are evolved through application of the Stokes theorem on cell
edges via a Constrained-Transport (CT) method. The multidimensional MHD source
terms required in the predictor step for high-order accuracy are applied in a
simplified form which reduces their complexity in three dimensions without loss
of accuracy or robustness. The algorithm is implemented on an AMR framework
which requires specific synchronization steps across refinement levels. These
include face-centered restriction and prolongation operations and a {\it
reflux-curl} operation, which maintains a solenoidal magnetic field across
refinement boundaries. The code is tested against a large suite of test
problems, including convergence tests in smooth flows, shock-tube tests,
classical two- and three-dimensional MHD tests, a three-dimensional shock-cloud
interaction problem and the formation of a cluster of galaxies in a fully
cosmological context. The magnetic field divergence is shown to remain
negligible throughout.Comment: 53 pages, 17 figs, under review by ApJ
The Dynamics of Rayleigh-Taylor Stable and Unstable Contact Discontinuities with Anisotropic Thermal Conduction
We study the effects of anisotropic thermal conduction along magnetic field
lines on an accelerated contact discontinuity in a weakly collisional plasma.
We first perform a linear stability analysis similar to that used to derive the
Rayleigh-Taylor instability (RTI) dispersion relation. We find that anisotropic
conduction is only important for compressible modes, as incompressible modes
are isothermal. Modes grow faster in the presence of anisotropic conduction,
but growth rates do not change by more than a factor of order unity. We next
run fully non-linear numerical simulations of a contact discontinuity with
anisotropic conduction. The non-linear evolution can be thought of as a
superposition of three physical effects: temperature diffusion due to vertical
conduction, the RTI, and the heat flux driven buoyancy instability (HBI). In
simulations with RTI-stable contact discontinuities, the temperature
discontinuity spreads due to vertical heat conduction. This occurs even for
initially horizontal magnetic fields due to the initial vertical velocity
perturbation and numerical mixing across the interface. The HBI slows this
temperature diffusion by reorienting initially vertical magnetic field lines to
a more horizontal geometry. In simulations with RTI-unstable contact
discontinuities, the dynamics are initially governed by temperature diffusion,
but the RTI becomes increasingly important at late times. We discuss the
possible application of these results to supernova remnants, solar prominences,
and cold fronts in galaxy clusters.Comment: 18 pages, 15 figures, submitted to MNRA
Traumatization and mental distress in long-term prisoners in Europe
This article investigates the prevalence of traumatization and mental distress
in a sample of 1055 male European long-term prisoners as part of a wider study
of the living conditions of prisoners serving sentences of at least five years
in Belgium, Croatia, Denmark, England, Finland, France, Germany, Lithuania,
Poland, Spain and Sweden. Data were collected in a written survey using the
Posttraumatic Diagnostic Scale (PDS), the Brief Symptom Inventory (BSI) as
well as questions on attempted suicide and auto-aggressive behaviour.
Participants experienced a mean of three traumatic events, with 14 per cent
developing a Posttraumatic Stress Disorder (PTSD) subsequently. In each
national sample, more than 50 per cent of the participants were in need of
treatment because of psychological symptoms and nearly one-third had attempted
suicide
Locally Perturbed Random Walks with Unbounded Jumps
In \cite{SzT}, D. Sz\'asz and A. Telcs have shown that for the diffusively
scaled, simple symmetric random walk, weak convergence to the Brownian motion
holds even in the case of local impurities if . The extension of their
result to finite range random walks is straightforward. Here, however, we are
interested in the situation when the random walk has unbounded range.
Concretely we generalize the statement of \cite{SzT} to unbounded random walks
whose jump distribution belongs to the domain of attraction of the normal law.
We do this first: for diffusively scaled random walks on having finite variance; and second: for random walks with distribution
belonging to the non-normal domain of attraction of the normal law. This result
can be applied to random walks with tail behavior analogous to that of the
infinite horizon Lorentz-process; these, in particular, have infinite variance,
and convergence to Brownian motion holds with the superdiffusive scaling.Comment: 16 page
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