Eldorado - Repository of the TU Dortmund
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A panel analysis of change in personal air travel behaviour in England between 2012 and 2019
(2024-12-03) Mattioli, Giulio; Scheiner, Joachim
Decarbonizing aviation is challenging as few scalable technological alternatives exist, and travel activity is increasing rapidly. It is thus essential to better understand the drivers of air travel behaviour. Previous cross-sectional research has identified a range of factors associated with individual air travel frequency. There is, however, a lack of longitudinal studies identifying the factors associated with change in air travel frequency on the individual level. This is in contrast with research on daily travel and car use, where ‘mobility biographies’ studies have identified the life-course factors associated with travel behaviour change. Our study contributes to filling this gap. We investigate the determinants of change in air travel frequency using data from two waves of the UK Household Longitudinal Survey (2012–2013 and 2018–2019), combined with geographical information at the neighbourhood level. With regression models, we assess the impact of changes in a wide range of factors including socio-demographic and economic situation; residential location; spatial dispersion of social networks; migration status; car ownership; and environmental attitudes. We find significant effects for several variables, including e.g., a negative effect of having children on air travel frequency, and a reduction in the number of flights in the first few years after migrating to the UK. We conclude by discussing how the findings can inform debates on: i) the impact of life-course events on travel behaviour; ii) the causal drivers of air travel frequency; iii) the drivers of air travel growth, and related implications in terms of inequality and ‘institutionalisation’ of air travel.
Augmented Lagrangian acceleration of global-in-time pressure Schur complement solvers for incompressible Oseen equations
(2024-03-28) Lohmann, Christoph; Turek, Stefan
This work is focused on an accelerated global-in-time solution strategy for the Oseen equations, which highly exploits the augmented Lagrangian methodology to improve the convergence behavior of the Schur complement iteration. The main idea of the solution strategy is to block the individual linear systems of equations at each time step into a single all-at-once saddle point problem. By elimination of all velocity unknowns, the resulting implicitly defined equation can then be solved using a global-in-time pressure Schur complement (PSC) iteration. To accelerate the convergence behavior of this iterative scheme, the augmented Lagrangian approach is exploited by modifying the momentum equation for all time steps in a strongly consistent manner. While the introduced discrete grad-div stabilization does not modify the solution of the discretized Oseen equations, the quality of customized PSC preconditioners drastically improves and, hence, guarantees a rapid convergence. This strategy comes at the cost that the involved auxiliary problem for the velocity field becomes ill conditioned so that standard iterative solution strategies are no longer efficient. Therefore, a highly specialized multigrid solver based on modified intergrid transfer operators and an additive block preconditioner is extended to solution of the all-at-once problem. The potential of the proposed overall solution strategy is discussed in several numerical studies as they occur in commonly used linearization techniques for the incompressible Navier–Stokes equations.
Application of the tight-binding method onto the Von Neumann equation
(2024-05-18) Abdi, Alan; Schulz, Dirk
This paper presents a numerical framework for the analysis of quantum devices based on the Von Neumann (VN) equation, which involves the concept of the Tight-Binding Method (TBM). The model is based on the application of the Tight-Binding Hamiltonian within Quantum Liouville Type Equations and has the advantage that the atomic structure of the materials used is taken into account. Furthermore, the influence of a Complex Absorbing Potential (CAP) as a complementary boundary condition and its essential contribution to the system stability with respect to the eigenvalue spectrum is discussed.
Bad local minima exist in the stochastic block model
(2024-11-11) Coja-Oghlan, Amin; Krieg, Lena; Lawnik, Johannes Christian; Scheftelowitsch, Olga
We study the disassortative stochastic block model with three communities, a well-studied model of graph partitioning and Bayesian inference for which detailed predictions based on the cavity method exist (Decelle et al. in Phys Rev E 84:066106, 2011). We provide strong evidence that for a part of the phase where efficient algorithms exist that approximately reconstruct the communities, inference based on maximum a posteriori (MAP) fails. In other words, we show that there exist modes of the posterior distribution that have a vanishing agreement with the ground truth. The proof is based on the analysis of a graph colouring algorithm from Achlioptas and Moore (J Comput Syst Sci 67:441–471, 2003).
A thermodynamically consistent phase transformation model for multiphase alloys
(2024-05-06) Noll, Isabelle; Bartel, Thorsten; Menzel, Andreas
Titan aluminium alloys belong to the group of –-alloys, which are used for many applications in industry due to their advantageous mechanical properties, e.g. for laser powder bed fusion (PBF-LB) processes. However, the composition of the crystal structure and the respective magnitude of the solid fraction highly influences the material properties of titan aluminium alloys. Specifically, the thermal history, i.e. the cooling rate, determines the phase composition and microstructure for example during heat treatment and PBF-LB processes. For that reason, the present work introduces a phase transformation framework based, amongst others, on energy densities and thermodynamically consistent evolution equations, which is able to capture the different material compositions resulting from cooling and heating rates. The evolution of the underlying phases is governed by a specifically designed dissipation function, the coefficients of which are determined by a parameter identification process based on available continuous cooling temperature (CCT) diagrams. In order to calibrate the model and its preparation for further applications such as the simulation of additive manufacturing processes, these CCT diagrams are computationally reconstructed. In contrast to empirical formulations, the developed thermodynamically consistent and physically sound model can straightforwardly be extended to further phase fractions and different materials. With this formulation, it is possible to predict not only the microstructure evolution during processes with high temperature gradients, as occurring in e.g. PBF-LB processes, but also the evolving strains during and at the end of the process.