Structural analysis of some sodium and alumina rich high-level nuclear waste glasses

Sodium- and aluminum-rich high-level nuclear waste glasses are prone to nepheline (NaAlSiO₄) crystallization. Since nepheline removes three moles of glass-forming oxides (Al₂O₃ and SiO₂) per mole of Na₂O, the formation of this phase can result in severe deterioration of the chemical durability in a given glass. The present study aims to investigate the relationships between the molecular-level structure and the crystallization behavior of sodium alumino-borosilicate-based simulated high-level nuclear waste glasses with infrared spectroscopy (FTIR) and X-ray diffraction, respectively. The molecular structure of most of the investigated glasses comprise a mixture of Q² and Q³ (Si) units while aluminum and boron are predominantly present in tetrahedral and trigonal coordination, respectively. The increasing boron content has been shown to suppress the nepheline formation in the glasses. The structural influence of various glass components on nepheline crystallization is discussed.     

Conversion of batch to molten glass, I: Volume expansion

Batches designed to simulate nuclear high-level waste glass were compressed into pellets that were heated at 5 K/min and photographed. Three types of batches were prepared, each with different amounts of nitrates and carbonates. The all-nitrate batches were prepared with varying amounts of sucrose. The mixed nitrate-carbonate batches were prepared with silica particles ranging in size from 5 to 195 μm. One batch containing only carbonates was also tested. Sucrose addition had little effect on expansion, while the size of silica was very influential. Sucrose addition reduced primary foam for batches containing 5-μm silica, but had no effect on batches containing larger particles. Excessive amounts of sucrose increased secondary foam. The 5-μm grains had the strongest effect, causing both primary and secondary foam to be generated, whereas only secondary foam was produced in batches with grains of 45 μm and larger. We suggest that the viscosity of the melt and the amount of gas evolved are the main influences on foam production. As more gas is produced in the melt and as the glass becomes less viscous, gas bubbles coalesce into larger cavities until the glass can no longer contain the bubbles and they burst, causing the foam to collapse.     

Reconstructing absorption and diffusion shape profiles in optical tomography by a level set technique

A shape reconstruction algorithm for optical tomography is introduced that uses a level-set formulation for the shapes. Evolution laws based on gradient directions for a cost functional are derived for two different level-set functions, one describing the absorption and one the diffusion parameter, as well as for the parameter values inside these shapes. Numerical experiments are presented in 2D that show that the new method is able to simultaneously recover shapes and contrast values of absorbing and scattering objects embedded in a moderately heterogeneous background medium from simulated noisy data.     

Sensitivity optimization in amplitude-modulated CW-EPR experiment

A sensitivity of recently developed method of amplitude-modulated continuous wave EPR (AM-CW-EPR) is studied depending on the parameters of the modulation field. The case of the significant saturation and high modulation frequency is addressed. It is found, that the rapid resonance passage effect is essential for AM-CW-EPR. However, its manifestation is different comparing to the conventional CW-EPR experiment. Both experimental data and numerical simulations support the enhancement of the AM-CW-EPR sensitivity under the rapid passage conditions for the modulating magnetic field, which is important for practical use of the method.     

Self-Gravitating Klein–Gordon Fields in Asymptotically Anti-de-Sitter Spacetimes

We initiate the study of the spherically symmetric Einstein–Klein–Gordon system in the presence of a negative cosmological constant, a model appearing frequently in the context of high-energy physics. Due to the lack of global hyperbolicity of the solutions, the natural formulation of dynamics is that of an initial boundary value problem, with boundary conditions imposed at null infinity. We prove a local well-posedness statement for this system, with the time of existence of the solutions depending only on an invariant H ²-type norm measuring the size of the Klein–Gordon field on the initial data. The proof requires the introduction of a renormalized system of equations and relies crucially on r-weighted estimates for the wave equation on asymptotically AdS spacetimes. The results provide the basis for our companion paper establishing the global asymptotic stability of Schwarzschild-Anti-de-Sitter within this system.     

Dynamics of a running gear with IRWs on curved tracks for a robust control development

As a major task of the DLR-internal project “Next Generation Train”, robust state feedback control with gain scheduling was sucessfully applied to guide the experimental running gear with independently rotating wheels (IRWs) at a 1:5 scaled roller rig, see [1]. However, the adaptation of the control structure to the 1:1 multibody model requires to additionally consider the properties of curved tracks. For that reason, an analytical model of a running gear with IRWs is deduced using Euler-Lagrange-equations and taking superelevation and track curvature into account. Furthermore, the complexity of the system is reduced to allow for a robust feedback control synthesis and feed-forward control including model inversion. Finally, the model is discussed and a first approach for a feed-forward control in transition curves is shown. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)